* [PATCH] virtio_net: invoke softirqs after __napi_schedule
@ 2012-05-16 7:57 Michael S. Tsirkin
2012-05-17 3:32 ` Rusty Russell
0 siblings, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2012-05-16 7:57 UTC (permalink / raw)
To: David Miller; +Cc: netdev, virtualization, linux-kernel, Michael S. Tsirkin
__napi_schedule might raise softirq but nothing
causes do_softirq to trigger, so it does not in fact
run. As a result,
the error message "NOHZ: local_softirq_pending 08"
sometimes occurs during boot of a KVM guest when the network service is
started and we are oom:
...
Bringing up loopback interface: [ OK ]
Bringing up interface eth0:
Determining IP information for eth0...NOHZ: local_softirq_pending 08
done.
[ OK ]
...
Further, receive queue processing might get delayed
indefinitely until some interrupt triggers:
virtio_net expected napi to be run immediately.
One way to cause do_softirq to be executed is by
invoking local_bh_enable(). As __napi_schedule is
normally called from bh or irq context, this
seems to make sense: disable bh before __napi_schedule
and enable afterwards.
Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
Tested-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
To test, one can hack try_fill_recv to always report oom.
I'm not sure it's not too late for 3.4, but we can try.
Rusty, could you review ASAP pls?
drivers/net/virtio_net.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index af8acc8..cbefe67 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -492,7 +492,9 @@ static void virtnet_napi_enable(struct virtnet_info *vi)
* We synchronize against interrupts via NAPI_STATE_SCHED */
if (napi_schedule_prep(&vi->napi)) {
virtqueue_disable_cb(vi->rvq);
+ local_bh_disable();
__napi_schedule(&vi->napi);
+ local_bh_enable();
}
}
--
MST
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
2012-05-16 7:57 [PATCH] virtio_net: invoke softirqs after __napi_schedule Michael S. Tsirkin
@ 2012-05-17 3:32 ` Rusty Russell
2012-05-17 3:40 ` David Miller
0 siblings, 1 reply; 3+ messages in thread
From: Rusty Russell @ 2012-05-17 3:32 UTC (permalink / raw)
To: Michael S. Tsirkin, David Miller
Cc: netdev, virtualization, linux-kernel, Michael S. Tsirkin
On Wed, 16 May 2012 10:57:13 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> __napi_schedule might raise softirq but nothing
> causes do_softirq to trigger, so it does not in fact
> run. As a result,
> the error message "NOHZ: local_softirq_pending 08"
> sometimes occurs during boot of a KVM guest when the network service is
> started and we are oom:
>
> ...
> Bringing up loopback interface: [ OK ]
> Bringing up interface eth0:
> Determining IP information for eth0...NOHZ: local_softirq_pending 08
> done.
> [ OK ]
> ...
>
> Further, receive queue processing might get delayed
> indefinitely until some interrupt triggers:
> virtio_net expected napi to be run immediately.
>
> One way to cause do_softirq to be executed is by
> invoking local_bh_enable(). As __napi_schedule is
> normally called from bh or irq context, this
> seems to make sense: disable bh before __napi_schedule
> and enable afterwards.
>
> Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
> Tested-by: Ulrich Obergfell <uobergfe@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>
> To test, one can hack try_fill_recv to always report oom.
> I'm not sure it's not too late for 3.4, but we can try.
> Rusty, could you review ASAP pls?
It's missing a big comment: it's a very complicated way of calling
do_softirq().
Indeed, this function is only used when we are not in interrupt
context. It's not hot at all, in any ideal scenario.
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
2012-05-17 3:32 ` Rusty Russell
@ 2012-05-17 3:40 ` David Miller
0 siblings, 0 replies; 3+ messages in thread
From: David Miller @ 2012-05-17 3:40 UTC (permalink / raw)
To: rusty; +Cc: netdev, virtualization, linux-kernel, mst
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Thu, 17 May 2012 13:02:53 +0930
> On Wed, 16 May 2012 10:57:13 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote:
>> __napi_schedule might raise softirq but nothing
>> causes do_softirq to trigger, so it does not in fact
>> run. As a result,
>> the error message "NOHZ: local_softirq_pending 08"
>> sometimes occurs during boot of a KVM guest when the network service is
>> started and we are oom:
>>
>> ...
>> Bringing up loopback interface: [ OK ]
>> Bringing up interface eth0:
>> Determining IP information for eth0...NOHZ: local_softirq_pending 08
>> done.
>> [ OK ]
>> ...
>>
>> Further, receive queue processing might get delayed
>> indefinitely until some interrupt triggers:
>> virtio_net expected napi to be run immediately.
>>
>> One way to cause do_softirq to be executed is by
>> invoking local_bh_enable(). As __napi_schedule is
>> normally called from bh or irq context, this
>> seems to make sense: disable bh before __napi_schedule
>> and enable afterwards.
>>
>> Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
>> Tested-by: Ulrich Obergfell <uobergfe@redhat.com>
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
...
> Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Michael, you're best to submit this directly to Linus as I just
made what I hope is my last push to him for 3.4 today.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-05-17 3:32 ` Rusty Russell
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