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Date: Wed, 24 Jul 2013 08:42:26 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff
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To: liu ping fan <qemulist@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Alex Bligh <alex@alex.org.uk>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>

Il 24/07/2013 03:28, liu ping fan ha scritto:
> On Tue, Jul 23, 2013 at 6:30 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> > Il 23/07/2013 04:53, liu ping fan ha scritto:
>>> >> The scenior I can figure out is if adopting timeout of poll, then when
>>> >> changing the deadline, we need to invoke poll, and set the new
>>> >> timeout, right?
>> >
>> > Yes, you need to call aio_notify so that poll is reinvoked.
>> >
> I try to list the difference between alarm_timer and timeout of poll.
> It includes thread-affinity, resolution and easy-use.
> 
> Most of all,  thread-affinity
> The main issue with alarm timer is the affinity of timer_t with
> threads. For linux, SIGEV_THREAD_ID has been supported for a very long
> time and we already associate the signal with the specified thread. So
> the only issue is left for other unix, we can emulate the affinity by
> using SIGEV_THREAD and repost the event to the specified thread.
> As to timeout of poll, it has the affinity of threads.
> 
> Resolution:
> alarm_timer provides higher resolution, but do we care about it?

With ppoll, is this true or just hearsay?

(Without ppoll, indeed setitimer has 1 us resolution while poll has 1
ms; too bad that select has other problems, because select has also 1 us
resolution).

Paolo

> easy-use:
> The reset of the deadline as mentioned.
> 
> Finally, I admit timeout of poll will save large chunk of platform-related code.