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Willem de Bruijn

2017-Sep-28 00:25 UTC

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

From: Willem de Bruijn <willemb at google.com>

Vhost-net has a hard limit on the number of zerocopy skbs in flight.
When reached, transmission stalls. Stalls cause latency, as well as
head-of-line blocking of other flows that do not use zerocopy.

Instead of stalling, revert to copy-based transmission.

Tested by sending two udp flows from guest to host, one with payload
of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
large flow is redirected to a netem instance with 1MBps rate limit
and deep 1000 entry queue.

  modprobe ifb
  ip link set dev ifb0 up
  tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit

  tc qdisc add dev tap0 ingress
  tc filter add dev tap0 parent ffff: protocol ip \
      u32 match ip dport 8000 0xffff \
      action mirred egress redirect dev ifb0

Before the delay, both flows process around 80K pps. With the delay,
before this patch, both process around 400. After this patch, the
large flow is still rate limited, while the small reverts to its
original rate. See also discussion in the first link, below.

The limit in vhost_exceeds_maxpend must be carefully chosen. When
vq->num >> 1, the flows remain correlated. This value happens to
correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller
fractions and ensure correctness also for much smaller values of
vq->num, by testing the min() of both explicitly. See also the
discussion in the second link below.

Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
Link:http://lkml.kernel.org/r/20170819064129.27272-1-den at klaipeden.com
Signed-off-by: Willem de Bruijn <willemb at google.com>
---
 drivers/vhost/net.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 58585ec8699e..50758602ae9d 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -436,8 +436,8 @@ static bool vhost_exceeds_maxpend(struct vhost_net *net)
 	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
 	struct vhost_virtqueue *vq = &nvq->vq;
 
-	return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV
-		== nvq->done_idx;
+	return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV >
+	       min(VHOST_MAX_PEND, vq->num >> 2);
 }
 
 /* Expects to be always run from workqueue - which acts as
@@ -480,12 +480,6 @@ static void handle_tx(struct vhost_net *net)
 		if (zcopy)
 			vhost_zerocopy_signal_used(net, vq);
 
-		/* If more outstanding DMAs, queue the work.
-		 * Handle upend_idx wrap around
-		 */
-		if (unlikely(vhost_exceeds_maxpend(net)))
-			break;
-
 		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
 						ARRAY_SIZE(vq->iov),
 						&out, &in);
@@ -509,6 +503,7 @@ static void handle_tx(struct vhost_net *net)
 		len = iov_length(vq->iov, out);
 		iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
 		iov_iter_advance(&msg.msg_iter, hdr_size);
+
 		/* Sanity check */
 		if (!msg_data_left(&msg)) {
 			vq_err(vq, "Unexpected header len for TX: "
@@ -519,8 +514,7 @@ static void handle_tx(struct vhost_net *net)
 		len = msg_data_left(&msg);
 
 		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
-				   && (nvq->upend_idx + 1) % UIO_MAXIOV !-				     
nvq->done_idx
+				   && !vhost_exceeds_maxpend(net)
 				   && vhost_net_tx_select_zcopy(net);
 
 		/* use msg_control to pass vhost zerocopy ubuf info to skb */
-- 
2.14.2.822.g60be5d43e6-goog

Willem de Bruijn

2017-Sep-28 00:33 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On Wed, Sep 27, 2017 at 8:25 PM, Willem de Bruijn
<willemdebruijn.kernel at gmail.com> wrote:> From: Willem de Bruijn <willemb at google.com>
>
> Vhost-net has a hard limit on the number of zerocopy skbs in flight.
> When reached, transmission stalls. Stalls cause latency, as well as
> head-of-line blocking of other flows that do not use zerocopy.
>
> Instead of stalling, revert to copy-based transmission.
>
> Tested by sending two udp flows from guest to host, one with payload
> of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
> large flow is redirected to a netem instance with 1MBps rate limit
> and deep 1000 entry queue.
>
>   modprobe ifb
>   ip link set dev ifb0 up
>   tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit
>
>   tc qdisc add dev tap0 ingress
>   tc filter add dev tap0 parent ffff: protocol ip \
>       u32 match ip dport 8000 0xffff \
>       action mirred egress redirect dev ifb0
>
> Before the delay, both flows process around 80K pps. With the delay,
> before this patch, both process around 400. After this patch, the
> large flow is still rate limited, while the small reverts to its
> original rate. See also discussion in the first link, below.
>
> The limit in vhost_exceeds_maxpend must be carefully chosen. When
> vq->num >> 1, the flows remain correlated. This value happens to
> correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller
> fractions and ensure correctness also for much smaller values of
> vq->num, by testing the min() of both explicitly. See also the
> discussion in the second link below.
>
>
Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
>From the same discussion thread: it would be good to expose statson the number of zerocopy skb sent and number completed without
copy.

To test this patch, I also added ethtool stats to tun and extended them
with two zerocopy counters. Then had tun override the uarg->callback
with its own and update the counters before calling the original callback.

The one useful datapoint I did not get out of that is why skbs would
revert to non-zerocopy: because of size, vhost_exceeds_maxpend
or vhost_net_tx_select_zcopy. The simplistic implementation with an
extra indirect function call and without percpu counters is also not
suitable for submission as is.

Jason Wang

2017-Sep-28 07:41 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On 2017?09?28? 08:25, Willem de Bruijn wrote:> From: Willem de Bruijn <willemb at google.com>
>
> Vhost-net has a hard limit on the number of zerocopy skbs in flight.
> When reached, transmission stalls. Stalls cause latency, as well as
> head-of-line blocking of other flows that do not use zerocopy.
>
> Instead of stalling, revert to copy-based transmission.
>
> Tested by sending two udp flows from guest to host, one with payload
> of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
> large flow is redirected to a netem instance with 1MBps rate limit
> and deep 1000 entry queue.
>
>    modprobe ifb
>    ip link set dev ifb0 up
>    tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit
>
>    tc qdisc add dev tap0 ingress
>    tc filter add dev tap0 parent ffff: protocol ip \
>        u32 match ip dport 8000 0xffff \
>        action mirred egress redirect dev ifb0
>
> Before the delay, both flows process around 80K pps. With the delay,
> before this patch, both process around 400. After this patch, the
> large flow is still rate limited, while the small reverts to its
> original rate. See also discussion in the first link, below.
>
> The limit in vhost_exceeds_maxpend must be carefully chosen. When
> vq->num >> 1, the flows remain correlated. This value happens to
> correspond to VHOST_MAX_PENDING for vq->num == 256.
Have you tested e.g vq->num = 512 or 1024?
>   Allow smaller
> fractions and ensure correctness also for much smaller values of
> vq->num, by testing the min() of both explicitly. See also the
> discussion in the second link below.
>
>
Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
> Link:http://lkml.kernel.org/r/20170819064129.27272-1-den at klaipeden.com
> Signed-off-by: Willem de Bruijn <willemb at google.com>
> ---
>   drivers/vhost/net.c | 14 ++++----------
>   1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 58585ec8699e..50758602ae9d 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -436,8 +436,8 @@ static bool vhost_exceeds_maxpend(struct vhost_net
*net)
>   	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>   	struct vhost_virtqueue *vq = &nvq->vq;
>   
> -	return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV
> -		== nvq->done_idx;
> +	return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV
>
> +	       min(VHOST_MAX_PEND, vq->num >> 2);
>   }
>   
>   /* Expects to be always run from workqueue - which acts as
> @@ -480,12 +480,6 @@ static void handle_tx(struct vhost_net *net)
>   		if (zcopy)
>   			vhost_zerocopy_signal_used(net, vq);
>   
> -		/* If more outstanding DMAs, queue the work.
> -		 * Handle upend_idx wrap around
> -		 */
> -		if (unlikely(vhost_exceeds_maxpend(net)))
> -			break;
> -
>   		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
>   						ARRAY_SIZE(vq->iov),
>   						&out, &in);
> @@ -509,6 +503,7 @@ static void handle_tx(struct vhost_net *net)
>   		len = iov_length(vq->iov, out);
>   		iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
>   		iov_iter_advance(&msg.msg_iter, hdr_size);
> +
Looks unnecessary. Other looks good.
>   		/* Sanity check */
>   		if (!msg_data_left(&msg)) {
>   			vq_err(vq, "Unexpected header len for TX: "
> @@ -519,8 +514,7 @@ static void handle_tx(struct vhost_net *net)
>   		len = msg_data_left(&msg);
>   
>   		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
> -				   && (nvq->upend_idx + 1) % UIO_MAXIOV !> -				     
nvq->done_idx
> +				   && !vhost_exceeds_maxpend(net)
>   				   && vhost_net_tx_select_zcopy(net);
>   
>   		/* use msg_control to pass vhost zerocopy ubuf info to skb */

Willem de Bruijn

2017-Sep-28 16:05 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On Thu, Sep 28, 2017 at 3:41 AM, Jason Wang <jasowang at redhat.com>
wrote:>
>
> On 2017?09?28? 08:25, Willem de Bruijn wrote:
>>
>> From: Willem de Bruijn <willemb at google.com>
>>
>> Vhost-net has a hard limit on the number of zerocopy skbs in flight.
>> When reached, transmission stalls. Stalls cause latency, as well as
>> head-of-line blocking of other flows that do not use zerocopy.
>>
>> Instead of stalling, revert to copy-based transmission.
>>
>> Tested by sending two udp flows from guest to host, one with payload
>> of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
>> large flow is redirected to a netem instance with 1MBps rate limit
>> and deep 1000 entry queue.
>>
>>    modprobe ifb
>>    ip link set dev ifb0 up
>>    tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit
>>
>>    tc qdisc add dev tap0 ingress
>>    tc filter add dev tap0 parent ffff: protocol ip \
>>        u32 match ip dport 8000 0xffff \
>>        action mirred egress redirect dev ifb0
>>
>> Before the delay, both flows process around 80K pps. With the delay,
>> before this patch, both process around 400. After this patch, the
>> large flow is still rate limited, while the small reverts to its
>> original rate. See also discussion in the first link, below.
>>
>> The limit in vhost_exceeds_maxpend must be carefully chosen. When
>> vq->num >> 1, the flows remain correlated. This value happens
to
>> correspond to VHOST_MAX_PENDING for vq->num == 256.
>
>
> Have you tested e.g vq->num = 512 or 1024?
I did test with 1024 previously, but let me run that again
with this patch applied.
>
>
>>   Allow smaller
>> fractions and ensure correctness also for much smaller values of
>> vq->num, by testing the min() of both explicitly. See also the
>> discussion in the second link below.
>>
>>
>>
Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
>> Link:http://lkml.kernel.org/r/20170819064129.27272-1-den at
klaipeden.com
>> Signed-off-by: Willem de Bruijn <willemb at google.com>
>> ---
>>   drivers/vhost/net.c | 14 ++++----------
>>   1 file changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 58585ec8699e..50758602ae9d 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -436,8 +436,8 @@ static bool vhost_exceeds_maxpend(struct vhost_net
>> *net)
>>         struct vhost_net_virtqueue *nvq =
&net->vqs[VHOST_NET_VQ_TX];
>>         struct vhost_virtqueue *vq = &nvq->vq;
>>   -     return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) %
UIO_MAXIOV
>> -               == nvq->done_idx;
>> +       return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) %
UIO_MAXIOV
>> >
>> +              min(VHOST_MAX_PEND, vq->num >> 2);
>>   }
>>     /* Expects to be always run from workqueue - which acts as
>> @@ -480,12 +480,6 @@ static void handle_tx(struct vhost_net *net)
>>                 if (zcopy)
>>                         vhost_zerocopy_signal_used(net, vq);
>>   -             /* If more outstanding DMAs, queue the work.
>> -                * Handle upend_idx wrap around
>> -                */
>> -               if (unlikely(vhost_exceeds_maxpend(net)))
>> -                       break;
>> -
>>                 head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
>>                                                 ARRAY_SIZE(vq->iov),
>>                                                 &out, &in);
>> @@ -509,6 +503,7 @@ static void handle_tx(struct vhost_net *net)
>>                 len = iov_length(vq->iov, out);
>>                 iov_iter_init(&msg.msg_iter, WRITE, vq->iov,
out, len);
>>                 iov_iter_advance(&msg.msg_iter, hdr_size);
>> +
>
>
> Looks unnecessary. Other looks good.
Oops, indeed. Thanks.

Michael S. Tsirkin

2017-Sep-29 19:38 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On Wed, Sep 27, 2017 at 08:25:56PM -0400, Willem de Bruijn
wrote:> From: Willem de Bruijn <willemb at google.com>
> 
> Vhost-net has a hard limit on the number of zerocopy skbs in flight.
> When reached, transmission stalls. Stalls cause latency, as well as
> head-of-line blocking of other flows that do not use zerocopy.
> 
> Instead of stalling, revert to copy-based transmission.
> 
> Tested by sending two udp flows from guest to host, one with payload
> of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
> large flow is redirected to a netem instance with 1MBps rate limit
> and deep 1000 entry queue.
> 
>   modprobe ifb
>   ip link set dev ifb0 up
>   tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit
> 
>   tc qdisc add dev tap0 ingress
>   tc filter add dev tap0 parent ffff: protocol ip \
>       u32 match ip dport 8000 0xffff \
>       action mirred egress redirect dev ifb0
> 
> Before the delay, both flows process around 80K pps. With the delay,
> before this patch, both process around 400. After this patch, the
> large flow is still rate limited, while the small reverts to its
> original rate. See also discussion in the first link, below.
> 
> The limit in vhost_exceeds_maxpend must be carefully chosen. When
> vq->num >> 1, the flows remain correlated. This value happens to
> correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller
> fractions and ensure correctness also for much smaller values of
> vq->num, by testing the min() of both explicitly. See also the
> discussion in the second link below.
> 
>
Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
> Link:http://lkml.kernel.org/r/20170819064129.27272-1-den at klaipeden.com
> Signed-off-by: Willem de Bruijn <willemb at google.com>
I'd like to see the effect on the non rate limited case though.
If guest is quick won't we have lots of copies then?

> ---
>  drivers/vhost/net.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 58585ec8699e..50758602ae9d 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -436,8 +436,8 @@ static bool vhost_exceeds_maxpend(struct vhost_net
*net)
>  	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>  	struct vhost_virtqueue *vq = &nvq->vq;
>  
> -	return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV
> -		== nvq->done_idx;
> +	return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV
>
> +	       min(VHOST_MAX_PEND, vq->num >> 2);
>  }
>  
>  /* Expects to be always run from workqueue - which acts as
> @@ -480,12 +480,6 @@ static void handle_tx(struct vhost_net *net)
>  		if (zcopy)
>  			vhost_zerocopy_signal_used(net, vq);
>  
> -		/* If more outstanding DMAs, queue the work.
> -		 * Handle upend_idx wrap around
> -		 */
> -		if (unlikely(vhost_exceeds_maxpend(net)))
> -			break;
> -
>  		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
>  						ARRAY_SIZE(vq->iov),
>  						&out, &in);
> @@ -509,6 +503,7 @@ static void handle_tx(struct vhost_net *net)
>  		len = iov_length(vq->iov, out);
>  		iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
>  		iov_iter_advance(&msg.msg_iter, hdr_size);
> +
>  		/* Sanity check */
>  		if (!msg_data_left(&msg)) {
>  			vq_err(vq, "Unexpected header len for TX: "
> @@ -519,8 +514,7 @@ static void handle_tx(struct vhost_net *net)
>  		len = msg_data_left(&msg);
>  
>  		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
> -				   && (nvq->upend_idx + 1) % UIO_MAXIOV !> -				     
nvq->done_idx
> +				   && !vhost_exceeds_maxpend(net)
>  				   && vhost_net_tx_select_zcopy(net);
>  
>  		/* use msg_control to pass vhost zerocopy ubuf info to skb */
> -- 
> 2.14.2.822.g60be5d43e6-goog

Willem de Bruijn

2017-Sep-30 01:25 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On Fri, Sep 29, 2017 at 3:38 PM, Michael S. Tsirkin <mst at redhat.com>
wrote:> On Wed, Sep 27, 2017 at 08:25:56PM -0400, Willem de Bruijn wrote:
>> From: Willem de Bruijn <willemb at google.com>
>>
>> Vhost-net has a hard limit on the number of zerocopy skbs in flight.
>> When reached, transmission stalls. Stalls cause latency, as well as
>> head-of-line blocking of other flows that do not use zerocopy.
>>
>> Instead of stalling, revert to copy-based transmission.
>>
>> Tested by sending two udp flows from guest to host, one with payload
>> of VHOST_GOODCOPY_LEN, the other too small for zerocopy (1B). The
>> large flow is redirected to a netem instance with 1MBps rate limit
>> and deep 1000 entry queue.
>>
>>   modprobe ifb
>>   ip link set dev ifb0 up
>>   tc qdisc add dev ifb0 root netem limit 1000 rate 1MBit
>>
>>   tc qdisc add dev tap0 ingress
>>   tc filter add dev tap0 parent ffff: protocol ip \
>>       u32 match ip dport 8000 0xffff \
>>       action mirred egress redirect dev ifb0
>>
>> Before the delay, both flows process around 80K pps. With the delay,
>> before this patch, both process around 400. After this patch, the
>> large flow is still rate limited, while the small reverts to its
>> original rate. See also discussion in the first link, below.
>>
>> The limit in vhost_exceeds_maxpend must be carefully chosen. When
>> vq->num >> 1, the flows remain correlated. This value happens
to
>> correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller
>> fractions and ensure correctness also for much smaller values of
>> vq->num, by testing the min() of both explicitly. See also the
>> discussion in the second link below.
>>
>>
Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g
at mail.gmail.com
>> Link:http://lkml.kernel.org/r/20170819064129.27272-1-den at
klaipeden.com
>> Signed-off-by: Willem de Bruijn <willemb at google.com>
>
> I'd like to see the effect on the non rate limited case though.
> If guest is quick won't we have lots of copies then?
Yes, but not significantly more than without this patch.

I ran 1, 10 and 100 flow tcp_stream throughput tests from a sender
in the guest to a receiver in the host.

To answer the other benchmark question first, I did not see anything
noteworthy when increasing vq->num from 256 to 1024.

With 1 and 10 flows without this patch all packets use zerocopy.
With the patch, less than 1% eschews zerocopy.

With 100 flows, even without this patch, 90+% of packets are copied.
Some zerocopy packets from vhost_net fail this test in tun.c

    if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)

Generating packets with up to 21 frags. I'm not sure yet why or
what the fraction of these packets is. But this in turn can
disable zcopy_used in vhost_net_tx_select_zcopy for a
larger share of packets:

        return !net->tx_flush &&
                net->tx_packets / 64 >= net->tx_zcopy_err;

Because the number of copied and zerocopy packets are the
same before and after the patch, so are the overall throughput
numbers.

kbuild test robot

2017-Sep-30 22:12 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

Hi Willem,

[auto build test WARNING on net-next/master]

url:   
https://github.com/0day-ci/linux/commits/Willem-de-Bruijn/vhost_net-do-not-stall-on-zerocopy-depletion/20171001-054709
config: x86_64-randconfig-x002-201740 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   In file included from include/linux/list.h:8:0,
                    from include/linux/wait.h:6,
                    from include/linux/eventfd.h:12,
                    from drivers/vhost/net.c:10:
   drivers/vhost/net.c: In function 'vhost_exceeds_maxpend':
   include/linux/kernel.h:772:16: warning: comparison of distinct pointer types
lacks a cast
     (void) (&min1 == &min2);   \
                   ^
   include/linux/kernel.h:775:2: note: in expansion of macro '__min'
     __min(typeof(x), typeof(y),   \
     ^~~~~>> drivers/vhost/net.c:440:9: note: in expansion of macro 'min'            min(VHOST_MAX_PEND, vq->num >> 2);
            ^~~

vim +/min +440 drivers/vhost/net.c

   433	
   434	static bool vhost_exceeds_maxpend(struct vhost_net *net)
   435	{
   436		struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
   437		struct vhost_virtqueue *vq = &nvq->vq;
   438	
   439		return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV
>
 > 440		       min(VHOST_MAX_PEND, vq->num >> 2);
   441	}
   442	

---
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kbuild test robot

2017-Sep-30 22:20 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

Hi Willem,

[auto build test WARNING on net-next/master]

url:   
https://github.com/0day-ci/linux/commits/Willem-de-Bruijn/vhost_net-do-not-stall-on-zerocopy-depletion/20171001-054709
config: tile-allyesconfig (attached as .config)
compiler: tilegx-linux-gcc (GCC) 4.6.2
reproduce:
        wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=tile 

All warnings (new ones prefixed by >>):

   drivers/vhost/net.c: In function
'vhost_exceeds_maxpend':>> drivers/vhost/net.c:440:9: warning: comparison of distinct pointer
types lacks a cast [enabled by default]
vim +440 drivers/vhost/net.c

   433	
   434	static bool vhost_exceeds_maxpend(struct vhost_net *net)
   435	{
   436		struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
   437		struct vhost_virtqueue *vq = &nvq->vq;
   438	
   439		return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV
>
 > 440		       min(VHOST_MAX_PEND, vq->num >> 2);
   441	}
   442	

---
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kbuild test robot

2017-Oct-01 00:09 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

Hi Willem,

[auto build test WARNING on net-next/master]

url:   
https://github.com/0day-ci/linux/commits/Willem-de-Bruijn/vhost_net-do-not-stall-on-zerocopy-depletion/20171001-054709
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)


vim +440 drivers/vhost/net.c

   433	
   434	static bool vhost_exceeds_maxpend(struct vhost_net *net)
   435	{
   436		struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
   437		struct vhost_virtqueue *vq = &nvq->vq;
   438	
   439		return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV
>
 > 440		       min(VHOST_MAX_PEND, vq->num >> 2);
   441	}
   442	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Michael S. Tsirkin

2017-Oct-01 03:20 UTC

head link

[PATCH net-next] vhost_net: do not stall on zerocopy depletion

On Sun, Oct 01, 2017 at 08:09:30AM +0800, kbuild test robot
wrote:> Hi Willem,
> 
> [auto build test WARNING on net-next/master]
> 
> url:   
https://github.com/0day-ci/linux/commits/Willem-de-Bruijn/vhost_net-do-not-stall-on-zerocopy-depletion/20171001-054709
> reproduce:
>         # apt-get install sparse
>         make ARCH=x86_64 allmodconfig
>         make C=1 CF=-D__CHECK_ENDIAN__
BTW __CHECK_ENDIAN__ is the default now, I think you can drop it from
your scripts.
> 
> sparse warnings: (new ones prefixed by >>)
> 
> 
> vim +440 drivers/vhost/net.c
> 
>    433	
>    434	static bool vhost_exceeds_maxpend(struct vhost_net *net)
>    435	{
>    436		struct vhost_net_virtqueue *nvq =
&net->vqs[VHOST_NET_VQ_TX];
>    437		struct vhost_virtqueue *vq = &nvq->vq;
>    438	
>    439		return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) %
UIO_MAXIOV >
>  > 440		       min(VHOST_MAX_PEND, vq->num >> 2);
>    441	}
>    442	
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology
Center
> https://lists.01.org/pipermail/kbuild-all                   Intel
Corporation

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