From: Tejun Heo <tj@kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH RFC] virtio_net: fix refill related races
Date: Tue, 20 Dec 2011 11:09:46 -0800 [thread overview]
Message-ID: <20111220190946.GD10752@google.com> (raw)
In-Reply-To: <20111220190908.GC25689@redhat.com>
Hello, Michael.
On Tue, Dec 20, 2011 at 09:09:08PM +0200, Michael S. Tsirkin wrote:
> Another question, wanted to make sure:
> virtnet_poll does schedule_delayed_work(&vi->refill, 0);
> separately refill work itself also does
> schedule_delayed_work(&vi->refill, HZ/2);
> If two such events happen twice, on different CPUs, we are still guaranteed
> the work will only run once, right?
No, it's not. Normal workqueues only guarantee non-reentrance on
local CPU. If you want to guarantee that only one instance of a given
item is executing across all CPUs, you need to use the nrt workqueue.
Thanks.
--
tejun
WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj@kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
Amit Shah <amit.shah@redhat.com>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] virtio_net: fix refill related races
Date: Tue, 20 Dec 2011 11:09:46 -0800 [thread overview]
Message-ID: <20111220190946.GD10752@google.com> (raw)
In-Reply-To: <20111220190908.GC25689@redhat.com>
Hello, Michael.
On Tue, Dec 20, 2011 at 09:09:08PM +0200, Michael S. Tsirkin wrote:
> Another question, wanted to make sure:
> virtnet_poll does schedule_delayed_work(&vi->refill, 0);
> separately refill work itself also does
> schedule_delayed_work(&vi->refill, HZ/2);
> If two such events happen twice, on different CPUs, we are still guaranteed
> the work will only run once, right?
No, it's not. Normal workqueues only guarantee non-reentrance on
local CPU. If you want to guarantee that only one instance of a given
item is executing across all CPUs, you need to use the nrt workqueue.
Thanks.
--
tejun
next prev parent reply other threads:[~2011-12-20 19:09 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-07 15:21 [PATCH RFC] virtio_net: fix refill related races Michael S. Tsirkin
2011-12-07 15:21 ` Michael S. Tsirkin
2011-12-08 4:37 ` Rusty Russell
2011-12-08 4:37 ` Rusty Russell
2011-12-08 4:37 ` Rusty Russell
2011-12-11 14:44 ` Michael S. Tsirkin
2011-12-11 14:44 ` Michael S. Tsirkin
2011-12-11 22:55 ` Rusty Russell
2011-12-11 22:55 ` Rusty Russell
2011-12-12 11:54 ` Michael S. Tsirkin
2011-12-12 11:54 ` Michael S. Tsirkin
2011-12-13 2:35 ` Rusty Russell
2011-12-13 2:35 ` Rusty Russell
2011-12-14 23:54 ` Tejun Heo
2011-12-14 23:54 ` Tejun Heo
2011-12-20 19:09 ` Michael S. Tsirkin
2011-12-20 19:09 ` Michael S. Tsirkin
2011-12-20 19:09 ` Tejun Heo [this message]
2011-12-20 19:09 ` Tejun Heo
2011-12-20 19:30 ` Michael S. Tsirkin
2011-12-20 19:30 ` Michael S. Tsirkin
2011-12-20 19:31 ` Tejun Heo
2011-12-20 19:31 ` Tejun Heo
2011-12-20 19:45 ` Michael S. Tsirkin
2011-12-20 19:45 ` Michael S. Tsirkin
2011-12-20 23:43 ` Rusty Russell
2011-12-20 23:43 ` Rusty Russell
2011-12-21 9:06 ` Michael S. Tsirkin
2011-12-21 9:06 ` Michael S. Tsirkin
2011-12-22 3:53 ` Rusty Russell
2011-12-22 3:53 ` Rusty Russell
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