From: David Miller <davem@davemloft.net>
To: rusty@rustcorp.com.au
Cc: netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, mst@redhat.com
Subject: Re: [PATCH] virtio_net: invoke softirqs after __napi_schedule
Date: Wed, 16 May 2012 23:40:53 -0400 (EDT) [thread overview]
Message-ID: <20120516.234053.248044235713127837.davem@davemloft.net> (raw)
In-Reply-To: <87vcjvzdlm.fsf@rustcorp.com.au>
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.
prev parent reply other threads:[~2012-05-17 3:40 UTC|newest]
Thread overview: 3+ 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
2012-05-17 3:32 ` Rusty Russell
2012-05-17 3:40 ` David Miller [this message]
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