From: Keir Fraser <keir@xen.org>
To: Wei Liu <wei.liu2@citrix.com>, David Vrabel <david.vrabel@citrix.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: Scalable Event Channel ABI design (draft A)
Date: Mon, 04 Feb 2013 22:16:21 +0000 [thread overview]
Message-ID: <CD35E3B5.5A03B%keir@xen.org> (raw)
In-Reply-To: <1360012076.7477.132.camel@zion.uk.xensource.com>
On 04/02/2013 21:07, "Wei Liu" <wei.liu2@citrix.com> wrote:
>> Concurrent access by Xen to the event queue must be protected by a
>> per-event queue spin lock.
>>
>
> I presume "E[n]" in the pseudo code is "E[p]"?
>
> Is this spin lock really a good idea? How many threads / cpus will spin
> on this lock? As [0] shows, contention on spin lock incurs heavy
> performance penalty.
>
> [0] https://lwn.net/Articles/530458/
Given that the critical region is small, the extra cache line contention for
the spinlock is probably not a big deal. Even in the current event-channel
design, we would get cache ping-pong on the event-channel bitmaps.
Consider 10k interrupts to a CPU would be a heavy amount. That's one every
100us. The event-channel delivery code described probably runs in less than
1us, even if memory accesses are horrible cache misses. The really highly
contended case shouldn't happen.
-- Keir
next prev parent reply other threads:[~2013-02-04 22:16 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-04 17:52 Scalable Event Channel ABI design (draft A) David Vrabel
2013-02-04 19:59 ` Keir Fraser
2013-02-05 14:48 ` David Vrabel
2013-02-05 15:16 ` Wei Liu
2013-02-05 18:05 ` George Dunlap
2013-02-05 18:57 ` David Vrabel
2013-02-05 19:03 ` Wei Liu
2013-02-06 11:32 ` George Dunlap
2013-02-06 13:53 ` Keir Fraser
2013-03-14 19:20 ` David Vrabel
2013-02-05 15:49 ` Keir Fraser
2013-02-05 15:54 ` David Vrabel
2013-02-05 16:11 ` Ian Campbell
2013-02-05 18:02 ` Keir Fraser
2013-02-06 9:38 ` Ian Campbell
2013-02-06 10:41 ` Keir Fraser
2013-02-06 10:42 ` Wei Liu
2013-02-06 10:52 ` Ian Campbell
2013-02-06 11:09 ` Wei Liu
2013-02-05 16:11 ` Keir Fraser
2013-02-06 11:46 ` Jan Beulich
2013-02-04 21:07 ` Wei Liu
2013-02-04 22:16 ` Keir Fraser [this message]
2013-02-05 18:36 ` David Vrabel
2013-02-05 16:10 ` Ian Campbell
2013-02-05 18:18 ` David Vrabel
2013-02-06 9:35 ` Ian Campbell
2013-02-06 9:13 ` Ian Campbell
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