thr3ads.net - Linux Virtualization - [PATCH V3 4/6] vhost_net: determine whether or not to use zerocopy at one time [Sep 2013]

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Michael S. Tsirkin

2013-Sep-04 11:59 UTC

[PATCH V3 4/6] vhost_net: determine whether or not to use zerocopy at one time

On Mon, Sep 02, 2013 at 04:40:59PM +0800, Jason Wang
wrote:> Currently, even if the packet length is smaller than VHOST_GOODCOPY_LEN, if
> upend_idx != done_idx we still set zcopy_used to true and rollback this
choice
> later. This could be avoided by determining zerocopy once by checking all
> conditions at one time before.
> 
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/vhost/net.c |   47 ++++++++++++++++++++---------------------------
>  1 files changed, 20 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 8a6dd0d..3f89dea 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -404,43 +404,36 @@ static void handle_tx(struct vhost_net *net)
>  			       iov_length(nvq->hdr, s), hdr_size);
>  			break;
>  		}
> -		zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||
> -				       nvq->upend_idx != nvq->done_idx);
> +
> +		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
> +				   && (nvq->upend_idx + 1) % UIO_MAXIOV !> +				     
nvq->done_idx
Thinking about this, this looks strange.
The original idea was that once we start doing zcopy, we keep
using the heads ring even for short packets until no zcopy is outstanding.

What's the logic behind (nvq->upend_idx + 1) % UIO_MAXIOV !=
nvq->done_idx
here?


> +				   && vhost_net_tx_select_zcopy(net);
>  
>  		/* use msg_control to pass vhost zerocopy ubuf info to skb */
>  		if (zcopy_used) {
> +			struct ubuf_info *ubuf;
> +			ubuf = nvq->ubuf_info + nvq->upend_idx;
> +
>  			vq->heads[nvq->upend_idx].id = head;
> -			if (!vhost_net_tx_select_zcopy(net) ||
> -			    len < VHOST_GOODCOPY_LEN) {
> -				/* copy don't need to wait for DMA done */
> -				vq->heads[nvq->upend_idx].len > -							VHOST_DMA_DONE_LEN;
> -				msg.msg_control = NULL;
> -				msg.msg_controllen = 0;
> -				ubufs = NULL;
> -			} else {
> -				struct ubuf_info *ubuf;
> -				ubuf = nvq->ubuf_info + nvq->upend_idx;
> -
> -				vq->heads[nvq->upend_idx].len > -					VHOST_DMA_IN_PROGRESS;
> -				ubuf->callback = vhost_zerocopy_callback;
> -				ubuf->ctx = nvq->ubufs;
> -				ubuf->desc = nvq->upend_idx;
> -				msg.msg_control = ubuf;
> -				msg.msg_controllen = sizeof(ubuf);
> -				ubufs = nvq->ubufs;
> -				kref_get(&ubufs->kref);
> -			}
> +			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
> +			ubuf->callback = vhost_zerocopy_callback;
> +			ubuf->ctx = nvq->ubufs;
> +			ubuf->desc = nvq->upend_idx;
> +			msg.msg_control = ubuf;
> +			msg.msg_controllen = sizeof(ubuf);
> +			ubufs = nvq->ubufs;
> +			kref_get(&ubufs->kref);
>  			nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
> -		} else
> +		} else {
>  			msg.msg_control = NULL;
> +			ubufs = NULL;
> +		}
>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(NULL, sock, &msg, len);
>  		if (unlikely(err < 0)) {
>  			if (zcopy_used) {
> -				if (ubufs)
> -					vhost_net_ubuf_put(ubufs);
> +				vhost_net_ubuf_put(ubufs);
>  				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
>  					% UIO_MAXIOV;
>  			}
> -- 
> 1.7.1

Jason Wang

2013-Sep-05 02:54 UTC

head link

[PATCH V3 4/6] vhost_net: determine whether or not to use zerocopy at one time

On 09/04/2013 07:59 PM, Michael S. Tsirkin wrote:> On Mon, Sep 02, 2013 at 04:40:59PM +0800, Jason Wang wrote:
>> Currently, even if the packet length is smaller than
VHOST_GOODCOPY_LEN, if
>> upend_idx != done_idx we still set zcopy_used to true and rollback this
choice
>> later. This could be avoided by determining zerocopy once by checking
all
>> conditions at one time before.
>>
>> Signed-off-by: Jason Wang <jasowang at redhat.com>
>> ---
>>  drivers/vhost/net.c |   47
++++++++++++++++++++---------------------------
>>  1 files changed, 20 insertions(+), 27 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 8a6dd0d..3f89dea 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -404,43 +404,36 @@ static void handle_tx(struct vhost_net *net)
>>  			       iov_length(nvq->hdr, s), hdr_size);
>>  			break;
>>  		}
>> -		zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||
>> -				       nvq->upend_idx != nvq->done_idx);
>> +
>> +		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
>> +				   && (nvq->upend_idx + 1) % UIO_MAXIOV !>> +				
nvq->done_idx
> Thinking about this, this looks strange.
> The original idea was that once we start doing zcopy, we keep
> using the heads ring even for short packets until no zcopy is outstanding.
What's the reason for keep using the heads ring?>
> What's the logic behind (nvq->upend_idx + 1) % UIO_MAXIOV !=
nvq->done_idx
> here?
Because we initialize both upend_idx and done_idx to zero, so upend_idx
!= done_idx could not be used to check whether or not the heads ring
were full.>> +				   && vhost_net_tx_select_zcopy(net);
>>  
>>  		/* use msg_control to pass vhost zerocopy ubuf info to skb */
>>  		if (zcopy_used) {
>> +			struct ubuf_info *ubuf;
>> +			ubuf = nvq->ubuf_info + nvq->upend_idx;
>> +
>>  			vq->heads[nvq->upend_idx].id = head;
>> -			if (!vhost_net_tx_select_zcopy(net) ||
>> -			    len < VHOST_GOODCOPY_LEN) {
>> -				/* copy don't need to wait for DMA done */
>> -				vq->heads[nvq->upend_idx].len >> -						
VHOST_DMA_DONE_LEN;
>> -				msg.msg_control = NULL;
>> -				msg.msg_controllen = 0;
>> -				ubufs = NULL;
>> -			} else {
>> -				struct ubuf_info *ubuf;
>> -				ubuf = nvq->ubuf_info + nvq->upend_idx;
>> -
>> -				vq->heads[nvq->upend_idx].len >> -				
VHOST_DMA_IN_PROGRESS;
>> -				ubuf->callback = vhost_zerocopy_callback;
>> -				ubuf->ctx = nvq->ubufs;
>> -				ubuf->desc = nvq->upend_idx;
>> -				msg.msg_control = ubuf;
>> -				msg.msg_controllen = sizeof(ubuf);
>> -				ubufs = nvq->ubufs;
>> -				kref_get(&ubufs->kref);
>> -			}
>> +			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
>> +			ubuf->callback = vhost_zerocopy_callback;
>> +			ubuf->ctx = nvq->ubufs;
>> +			ubuf->desc = nvq->upend_idx;
>> +			msg.msg_control = ubuf;
>> +			msg.msg_controllen = sizeof(ubuf);
>> +			ubufs = nvq->ubufs;
>> +			kref_get(&ubufs->kref);
>>  			nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
>> -		} else
>> +		} else {
>>  			msg.msg_control = NULL;
>> +			ubufs = NULL;
>> +		}
>>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>>  		err = sock->ops->sendmsg(NULL, sock, &msg, len);
>>  		if (unlikely(err < 0)) {
>>  			if (zcopy_used) {
>> -				if (ubufs)
>> -					vhost_net_ubuf_put(ubufs);
>> +				vhost_net_ubuf_put(ubufs);
>>  				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
>>  					% UIO_MAXIOV;
>>  			}
>> -- 
>> 1.7.1
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Michael S. Tsirkin

2013-Sep-23 07:16 UTC

head link

[PATCH V3 4/6] vhost_net: determine whether or not to use zerocopy at one time

On Thu, Sep 05, 2013 at 10:54:44AM +0800, Jason Wang
wrote:> On 09/04/2013 07:59 PM, Michael S. Tsirkin wrote:
> > On Mon, Sep 02, 2013 at 04:40:59PM +0800, Jason Wang wrote:
> >> Currently, even if the packet length is smaller than
VHOST_GOODCOPY_LEN, if
> >> upend_idx != done_idx we still set zcopy_used to true and rollback
this choice
> >> later. This could be avoided by determining zerocopy once by
checking all
> >> conditions at one time before.
> >>
> >> Signed-off-by: Jason Wang <jasowang at redhat.com>
> >> ---
> >>  drivers/vhost/net.c |   47
++++++++++++++++++++---------------------------
> >>  1 files changed, 20 insertions(+), 27 deletions(-)
> >>
> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >> index 8a6dd0d..3f89dea 100644
> >> --- a/drivers/vhost/net.c
> >> +++ b/drivers/vhost/net.c
> >> @@ -404,43 +404,36 @@ static void handle_tx(struct vhost_net *net)
> >>  			       iov_length(nvq->hdr, s), hdr_size);
> >>  			break;
> >>  		}
> >> -		zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||
> >> -				       nvq->upend_idx != nvq->done_idx);
> >> +
> >> +		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
> >> +				   && (nvq->upend_idx + 1) % UIO_MAXIOV !>
>> +				      nvq->done_idx
> > Thinking about this, this looks strange.
> > The original idea was that once we start doing zcopy, we keep
> > using the heads ring even for short packets until no zcopy is
outstanding.
> 
> What's the reason for keep using the heads ring?
To keep completions in order.
> >
> > What's the logic behind (nvq->upend_idx + 1) % UIO_MAXIOV !=
nvq->done_idx
> > here?
> 
> Because we initialize both upend_idx and done_idx to zero, so upend_idx
> != done_idx could not be used to check whether or not the heads ring
> were full.
But what does ring full have to do with zerocopy use?
> >> +				   && vhost_net_tx_select_zcopy(net);
> >>  
> >>  		/* use msg_control to pass vhost zerocopy ubuf info to skb */
> >>  		if (zcopy_used) {
> >> +			struct ubuf_info *ubuf;
> >> +			ubuf = nvq->ubuf_info + nvq->upend_idx;
> >> +
> >>  			vq->heads[nvq->upend_idx].id = head;
> >> -			if (!vhost_net_tx_select_zcopy(net) ||
> >> -			    len < VHOST_GOODCOPY_LEN) {
> >> -				/* copy don't need to wait for DMA done */
> >> -				vq->heads[nvq->upend_idx].len > >> -						
VHOST_DMA_DONE_LEN;
> >> -				msg.msg_control = NULL;
> >> -				msg.msg_controllen = 0;
> >> -				ubufs = NULL;
> >> -			} else {
> >> -				struct ubuf_info *ubuf;
> >> -				ubuf = nvq->ubuf_info + nvq->upend_idx;
> >> -
> >> -				vq->heads[nvq->upend_idx].len > >> -				
VHOST_DMA_IN_PROGRESS;
> >> -				ubuf->callback = vhost_zerocopy_callback;
> >> -				ubuf->ctx = nvq->ubufs;
> >> -				ubuf->desc = nvq->upend_idx;
> >> -				msg.msg_control = ubuf;
> >> -				msg.msg_controllen = sizeof(ubuf);
> >> -				ubufs = nvq->ubufs;
> >> -				kref_get(&ubufs->kref);
> >> -			}
> >> +			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
> >> +			ubuf->callback = vhost_zerocopy_callback;
> >> +			ubuf->ctx = nvq->ubufs;
> >> +			ubuf->desc = nvq->upend_idx;
> >> +			msg.msg_control = ubuf;
> >> +			msg.msg_controllen = sizeof(ubuf);
> >> +			ubufs = nvq->ubufs;
> >> +			kref_get(&ubufs->kref);
> >>  			nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
> >> -		} else
> >> +		} else {
> >>  			msg.msg_control = NULL;
> >> +			ubufs = NULL;
> >> +		}
> >>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
> >>  		err = sock->ops->sendmsg(NULL, sock, &msg, len);
> >>  		if (unlikely(err < 0)) {
> >>  			if (zcopy_used) {
> >> -				if (ubufs)
> >> -					vhost_net_ubuf_put(ubufs);
> >> +				vhost_net_ubuf_put(ubufs);
> >>  				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
> >>  					% UIO_MAXIOV;
> >>  			}
> >> -- 
> >> 1.7.1
> > --
> > To unsubscribe from this list: send the line "unsubscribe
kvm" in
> > the body of a message to majordomo at vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html

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