From: Pavel Machek <pavel@suse.cz>
To: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
"arjan@infradead.org" <arjan@infradead.org>
Subject: Re: [RFC] Imprecise timers.
Date: Tue, 12 Aug 2008 14:00:31 +0200 [thread overview]
Message-ID: <20080812120031.GD8806@elf.ucw.cz> (raw)
In-Reply-To: <20080811173526.GA28661@linux-os.sc.intel.com>
Hi!
> > > >which will run some time later when the CPU happens to be awake. And a
> > > >non-deferrable timer at the hard deadline, to ensure it really does
> > > >happen by then.
> > > >
> > >
> > > One concern I have is drivers using range_timers thinking that they need
> > > some upper bound, while all they need is a simple deferrable timer. With that
> > > we will have multiple timers waking up the CPU all the time (say, on
> > > different CPUs) problem again. Even without the timers waking up all
> >
> > I don't get it. Who has timers that can be deferred forever? At that
> > point they may simply not set the timer at all, right?
> >
>
> I don't think I said drivers have or need timers that can be deferred forever.
>
> My point is, is it worth the overhead of setting and deleting additional timer,
> just because drivers think that they need to use this new interface,
> need to set a upper bound and come up with random upper bounds.
> Apart from the overhead of setup and teardown we will somewhat negate the
> benefits of deferrable timers as the upper bound hard timers can fire at
> different times waking up the CPUs frequently.
> I understand that some drivers need this kind of upper limit. I am not sure
> whether all drivers need it and if not, how can we restrict drivers from using
> this when they don't really need it.
Do you have example of driver that does NOT need upper limit?
Like... lets take ATA.
submit_command()
if command is not back in ~5 seconds, it probably timed out.
So you set soft limit to 5 seconds, and hard limit to 10. You
definitely want user to know something is wrong after 10 seconds,
right?
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2008-08-12 13:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-22 3:02 [RFC] Imprecise timers David Woodhouse
2008-07-22 3:05 ` [RFC] schedule_timeout_range() David Woodhouse
2008-07-22 3:56 ` Nick Piggin
2008-07-22 4:12 ` David Woodhouse
2008-07-22 4:26 ` Arjan van de Ven
2008-07-22 4:34 ` David Woodhouse
2008-07-22 4:33 ` Nick Piggin
2008-07-22 4:45 ` David Woodhouse
2008-07-22 4:50 ` Nick Piggin
2008-07-22 4:58 ` David Woodhouse
2008-07-22 5:35 ` Jan Engelhardt
2008-07-22 4:33 ` Arjan van de Ven
2008-07-22 7:19 ` [RFC] Imprecise timers Rene Herman
2008-07-22 12:54 ` Arjan van de Ven
2008-07-22 14:04 ` Rene Herman
2008-07-29 0:36 ` Pallipadi, Venkatesh
2008-08-09 12:54 ` Pavel Machek
2008-08-11 17:35 ` Venki Pallipadi
2008-08-12 12:00 ` Pavel Machek [this message]
2008-08-12 18:11 ` Venki Pallipadi
2008-08-12 21:55 ` Alan Cox
2008-08-12 21:58 ` Pavel Machek
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