linux-kernel - Re: [patch 0/5] Nano/Microsecond resolution for select() and poll()

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Message-ID: <20080829091229.1ddfc92d@infradead.org>
Date:	Fri, 29 Aug 2008 09:12:29 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...x.de,
	torvalds@...ux-foundation.org,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [patch 0/5] Nano/Microsecond resolution for select() and poll()

On Fri, 29 Aug 2008 17:54:27 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> On Friday 29 August 2008, Arjan van de Ven wrote:
> 
> > With this patch series, the internals of select() and poll()
> > interfaces are changed such that they work on the nanosecond level
> > (using hrtimers). The userspace interface for select() is in
> > microseconds, for pselect() and ppoll() this is in nanoseconds.
> 
> Nice work, seems a lot better thought through than my previous
> attempt [1], which unfortunately never saw any reactions.
>  
> > even though poll() (as opposed to ppoll()) only accepts milliseconds
> > as userspace interface, the behavior will still improve because the
> > current time no longer needs to be rounded up to the next jiffie,
> > so on average a 500 milliseconds behavior improvement.
> 
> That would be 500 microseconds I think.
> 
> > I'd like to get rid of the jiffies timeout entirely over time, and
> > only use hrtimers (makes the code a lot nicer) but that's for now
> > a separate step, first I'd like to see how this change pans out. 
> 
> You mean entirely entirely getting rid of jiffies in the kernel, or
> just with user facing interfaces like epoll_wait, rt_sigtimedwait etc?

I meant actually just in the select() and poll() code; right now it is
sort of dual-brained, I'd like to eventually be able to get rid of that
and just use hrtimers for select() and poll() always

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