From: Rusty Russell <rusty@rustcorp.com.au>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
Date: Thu, 17 May 2012 13:02:53 +0930 [thread overview]
Message-ID: <87vcjvzdlm.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20120516075712.GA2921@redhat.com>
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>
WARNING: multiple messages have this Message-ID (diff)
From: Rusty Russell <rusty@rustcorp.com.au>
To: "Michael S. Tsirkin" <mst@redhat.com>,
David Miller <davem@davemloft.net>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
Date: Thu, 17 May 2012 13:02:53 +0930 [thread overview]
Message-ID: <87vcjvzdlm.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20120516075712.GA2921@redhat.com>
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>
WARNING: multiple messages have this Message-ID (diff)
From: Rusty Russell <rusty@rustcorp.com.au>
To: "Michael S. Tsirkin" <mst@redhat.com>,
David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
Date: Thu, 17 May 2012 13:02:53 +0930 [thread overview]
Message-ID: <87vcjvzdlm.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20120516075712.GA2921@redhat.com>
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>
next prev parent reply other threads:[~2012-05-17 3:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-16 7:57 [PATCH] virtio_net: invoke softirqs after __napi_schedule Michael S. Tsirkin
2012-05-16 7:57 ` Michael S. Tsirkin
2012-05-17 3:32 ` Rusty Russell [this message]
2012-05-17 3:32 ` Rusty Russell
2012-05-17 3:32 ` Rusty Russell
2012-05-17 3:40 ` David Miller
2012-05-17 3:40 ` David Miller
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