linux-kernel - Re: [PATCH 12/13] hrtimer: create a "timer

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Message-ID: <20080902060323.70245b83@infradead.org>
Date:	Tue, 2 Sep 2008 06:03:23 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Pavel Machek <pavel@...e.cz>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	dwmw2@...radead.org, drepper@...hat.com, mingo@...e.hu,
	tglx@...x.de
Subject: Re: [PATCH 12/13] hrtimer: create a "timer_slack" field in the task
 struct

On Tue, 2 Sep 2008 12:04:39 +0200
Pavel Machek <pavel@...e.cz> wrote:

> Hi!
> 
> > From: Arjan van de Ven <arjan@...ux.intel.com>
> > Subject: [PATCH] hrtimer: create a "timer_slack" field in the task
> > struct
> > 
> > We want to be able to control the default "rounding" that is used by
> > select() and poll() and friends. This is a per process property
> > (so that we can have a "nice" like program to start certain
> > programs with a looser or stricter rounding) that can be set/get
> > via a prctl().
> > 
> > For this purpose, a field called "timer_slack_ns" is added to the
> > task struct. In addition, a field called "default_timer_slack"ns"
> > is added so that tasks easily can temporarily to a more/less
> > accurate slack and then back to the default.
> 
> Is this a good idea? IMO it should be per-syscall, not per
> application.

Yes it would be nice to have new syscalls for this
and no, nobody and nothing would use them.

THe really big advantag of this default-from-task-struct is that you
can have a program similar to "nice" that allows you to run an existing
program at a specified granularity (say, a version of acroread that has
a really high wakeup count but you still want to save power)

> Threads would certainly like private values...

of course these are per thread.. they're in the task struct after all 

> and this makes really ugly interface.

prctl() is ugly?

> 
> ...plus it bloats task struct.
> 
> ...where did the sys_indirect proposals go? We created new syscalls,
> right?

... which nobody uses today.
It's not just new syscalls, it's a new glibc api as well at that point.


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