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Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff
Date: Wed, 24 Jul 2013 09:54:57 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7

Il 24/07/2013 09:43, liu ping fan ha scritto:
> Paid some time to dig the kernel code, and find out that the
> resolution lost by timeout of poll/select..etc is cause by the timeout
> is a slack region.
> See code in
> do_poll()
>    if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
> Notice the slack param, it causes the lose of resolution.
> The process default slack time  inherits from init_task and it is
>       .timer_slack_ns = 50000, /* 50 usec default slack */
> But we can fix it by PR_SET_TIMERSLACK to decrease it for select/poll/...

Right, good catch.  I just learnt about PR_SET_TIMERSLACK. :)

Alex, can you add it to your series?  (Note that you must set a timer
slack of 1, because 0 is interpreted as "default").

> So ppoll with timerslack adjustment will meet our requirement. But
> what about other non-linux system?

They might have their own mechanism similar to PR_SET_TIMERSLACK.


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