Toshiaki Makita
2017-Dec-07 04:15 UTC
[PATCH net-next] virtio_net: Disable interrupts if napi_complete_done rescheduled napi
Since commit 39e6c8208d7b ("net: solve a NAPI race") napi has been
able
to be rescheduled within napi_complete_done() even in non-busypoll case,
but virtnet_poll() always enabled interrupts before complete, and when
napi was rescheduled within napi_complete_done() it did not disable
interrupts.
This caused more interrupts when event idx is disabled.
According to commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ
processing") we cannot place virtqueue_enable_cb_prepare() after
NAPI_STATE_SCHED is cleared, so disable interrupts again if
napi_complete_done() returned false.
Tested with vhost-user of OVS 2.7 on host, which does not have the event
idx feature.
* Before patch:
$ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.150.253 () port 0 AF_INET
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
212992 1472 60.00 32763206 0 6430.32
212992 60.00 23384299 4589.56
Interrupts on guest: 9872369
Packets/interrupt: 2.37
* After patch
$ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.150.253 () port 0 AF_INET
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
212992 1472 60.00 32794646 0 6436.49
212992 60.00 32793501 6436.27
Interrupts on guest: 4941299
Packets/interrupt: 6.64
Signed-off-by: Toshiaki Makita <makita.toshiaki at lab.ntt.co.jp>
---
drivers/net/virtio_net.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 19a985e..c0db48d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -261,9 +261,12 @@ static void virtqueue_napi_complete(struct napi_struct
*napi,
int opaque;
opaque = virtqueue_enable_cb_prepare(vq);
- if (napi_complete_done(napi, processed) &&
- unlikely(virtqueue_poll(vq, opaque)))
- virtqueue_napi_schedule(napi, vq);
+ if (napi_complete_done(napi, processed)) {
+ if (unlikely(virtqueue_poll(vq, opaque)))
+ virtqueue_napi_schedule(napi, vq);
+ } else {
+ virtqueue_disable_cb(vq);
+ }
}
static void skb_xmit_done(struct virtqueue *vq)
--
1.8.3.1
Michael S. Tsirkin
2017-Dec-07 05:09 UTC
[PATCH net-next] virtio_net: Disable interrupts if napi_complete_done rescheduled napi
On Thu, Dec 07, 2017 at 01:15:15PM +0900, Toshiaki Makita wrote:> Since commit 39e6c8208d7b ("net: solve a NAPI race") napi has been able > to be rescheduled within napi_complete_done() even in non-busypoll case, > but virtnet_poll() always enabled interrupts before complete, and when > napi was rescheduled within napi_complete_done() it did not disable > interrupts. > This caused more interrupts when event idx is disabled. > > According to commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ > processing") we cannot place virtqueue_enable_cb_prepare() after > NAPI_STATE_SCHED is cleared, so disable interrupts again if > napi_complete_done() returned false. > > Tested with vhost-user of OVS 2.7 on host, which does not have the event > idx feature. > > * Before patch: > > $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472 > MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET > Socket Message Elapsed Messages > Size Size Time Okay Errors Throughput > bytes bytes secs # # 10^6bits/sec > > 212992 1472 60.00 32763206 0 6430.32 > 212992 60.00 23384299 4589.56 > > Interrupts on guest: 9872369 > Packets/interrupt: 2.37 > > * After patch > > $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472 > MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET > Socket Message Elapsed Messages > Size Size Time Okay Errors Throughput > bytes bytes secs # # 10^6bits/sec > > 212992 1472 60.00 32794646 0 6436.49 > 212992 60.00 32793501 6436.27 > > Interrupts on guest: 4941299 > Packets/interrupt: 6.64 > > Signed-off-by: Toshiaki Makita <makita.toshiaki at lab.ntt.co.jp>Acked-by: Michael S. Tsirkin <mst at redhat.com> it might make sense in net and not -next since tx napi regressed performance in some configs, this might bring it back at least partially. Jason - what do you think?> --- > drivers/net/virtio_net.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 19a985e..c0db48d 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -261,9 +261,12 @@ static void virtqueue_napi_complete(struct napi_struct *napi, > int opaque; > > opaque = virtqueue_enable_cb_prepare(vq); > - if (napi_complete_done(napi, processed) && > - unlikely(virtqueue_poll(vq, opaque))) > - virtqueue_napi_schedule(napi, vq); > + if (napi_complete_done(napi, processed)) { > + if (unlikely(virtqueue_poll(vq, opaque))) > + virtqueue_napi_schedule(napi, vq); > + } else { > + virtqueue_disable_cb(vq); > + } > } > > static void skb_xmit_done(struct virtqueue *vq) > -- > 1.8.3.1 >
Jason Wang
2017-Dec-07 07:08 UTC
[PATCH net-next] virtio_net: Disable interrupts if napi_complete_done rescheduled napi
On 2017?12?07? 13:09, Michael S. Tsirkin wrote:> On Thu, Dec 07, 2017 at 01:15:15PM +0900, Toshiaki Makita wrote: >> Since commit 39e6c8208d7b ("net: solve a NAPI race") napi has been able >> to be rescheduled within napi_complete_done() even in non-busypoll case, >> but virtnet_poll() always enabled interrupts before complete, and when >> napi was rescheduled within napi_complete_done() it did not disable >> interrupts. >> This caused more interrupts when event idx is disabled. >> >> According to commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ >> processing") we cannot place virtqueue_enable_cb_prepare() after >> NAPI_STATE_SCHED is cleared, so disable interrupts again if >> napi_complete_done() returned false. >> >> Tested with vhost-user of OVS 2.7 on host, which does not have the event >> idx feature. >> >> * Before patch: >> >> $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472 >> MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET >> Socket Message Elapsed Messages >> Size Size Time Okay Errors Throughput >> bytes bytes secs # # 10^6bits/sec >> >> 212992 1472 60.00 32763206 0 6430.32 >> 212992 60.00 23384299 4589.56 >> >> Interrupts on guest: 9872369 >> Packets/interrupt: 2.37 >> >> * After patch >> >> $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472 >> MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET >> Socket Message Elapsed Messages >> Size Size Time Okay Errors Throughput >> bytes bytes secs # # 10^6bits/sec >> >> 212992 1472 60.00 32794646 0 6436.49 >> 212992 60.00 32793501 6436.27 >> >> Interrupts on guest: 4941299 >> Packets/interrupt: 6.64 >> >> Signed-off-by: Toshiaki Makita <makita.toshiaki at lab.ntt.co.jp> > Acked-by: Michael S. Tsirkin <mst at redhat.com> > > it might make sense in net and not -next since tx napi regressed performance > in some configs, this might bring it back at least partially. > Jason - what do you think?No sure, the regression I saw was tested with event idx on. And virtqueue_disable_cb() does almost nothing for event idx (or even a little bit slower). The patch looks good. Acked-by: Jason Wang <jasowang at redhat.com>> >> --- >> drivers/net/virtio_net.c | 9 ++++++--- >> 1 file changed, 6 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 19a985e..c0db48d 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -261,9 +261,12 @@ static void virtqueue_napi_complete(struct napi_struct *napi, >> int opaque; >> >> opaque = virtqueue_enable_cb_prepare(vq); >> - if (napi_complete_done(napi, processed) && >> - unlikely(virtqueue_poll(vq, opaque))) >> - virtqueue_napi_schedule(napi, vq); >> + if (napi_complete_done(napi, processed)) { >> + if (unlikely(virtqueue_poll(vq, opaque))) >> + virtqueue_napi_schedule(napi, vq); >> + } else { >> + virtqueue_disable_cb(vq); >> + } >> } >> >> static void skb_xmit_done(struct virtqueue *vq) >> -- >> 1.8.3.1 >>
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