linux-kernel - Re: [PATCH v2 0/3] Deferrable timers support for timerfd API

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Date:	Mon, 27 Jan 2014 11:12:24 +0400
From:	Alexey Perevalov <a.perevalov@...sung.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
	anton@...msg.org, kyungmin.park@...sung.com,
	akpm@...ux-foundation.org, cw00.choi@...sung.com,
	Alexey Perevalov <a.perevalov@...sung.com>
Subject: Re: [PATCH v2 0/3] Deferrable timers support for timerfd API

Dear Thomas,
could you please comment John's question (see bellow) regarding flags.

On 01/21/2014 11:12 PM, John Stultz wrote:
> On 01/13/2014 02:43 AM, Alexey Perevalov wrote:
>> Hello dear community.
>>
>> This is reworked patch set of original Anton's Vorontsov
>> proposal regarding unified deferrable timers in the user space.
>> http://lwn.net/Articles/514707/
>>
>>
>> I decided to resubmit it due we found it usefull for us too.
>>
>> timerfd was modified since Anton's commit, Alarm support was added.
>> This isn't only rebase. Anton's previous version used deferrable timer
>> in couple with hrtimer. This version uses only deferrable timer. It
>> mean the behaviour of overrun number is different.
>> e.g. if you don't poll one second timer for a 10 seconds - you'll get
>> 10 overruns with hrtimer, but for deferrable timer it could be another value.
>>
> Sorry, last week was a little crazy and I didn't get a chance to closely
> review this. But looking at this my major conceptual objection with the
> previous patchset (introducing the new clockid) is gone.
>
> My remaining conceptual concern here is that the TIMER_DEFERRABLE flag
> is a timerfd only construct here, and I worry we should make sure we
> think this through well enough that the same functionality can be
> supported via other timer interfaces (like clock_nanosleep, etc), which
> may mean the functionality should be pushed more deeply into the hrtimer
> subsystem.
>
> So main suggestion here is to make sure you cc Thomas Gleixner on future
> iterations, so he can provide some thoughts on what the best approach
> might be here. I know he also has some plans that might collide with the
> jiffies_to_ktime work.
>
> Thomas: Any thought here? Should we be trying to unify the timerfd flags
> and the posix timer flags (specifically things like TIMER_CANCEL_ON_SET,
> which is currently timerfd-only)?  Should a deferrable flag be added to
> the hrtimer core or left to the timer wheel?
>
> thanks
> -john
>


-- 
Best regards,
Alexey Perevalov
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