From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Robert Love <rml@novell.com>
Cc: Jeff Garzik <jgarzik@pobox.com>,
Roland Dreier <roland@topspin.com>,
linux-kernel@vger.kernel.org
Subject: Re: Preempt? (was Re: Cannot enable DMA on SATA drive (SCSI-libsata, VIA SATA))
Date: Wed, 06 Oct 2004 12:30:47 +1000 [thread overview]
Message-ID: <416358D7.6080609@yahoo.com.au> (raw)
In-Reply-To: <1097028459.5062.104.camel@localhost>
Robert Love wrote:
> On Tue, 2004-10-05 at 21:55 -0400, Jeff Garzik wrote:
>
>
>>As opposed to fixing drivers??? Please fix the drivers and code first.
>
>
> No, definitely not, dude. Fixes for anything--drivers include--is never
> superseded by anything else, even the eternal quest for "low latency."
>
>
>>>sprinkling cond_resched() hacks all over the kernel.
>>
>>cond_resched() is not the only solution.
>
>
> Indeed. Most other solutions (fixing algorithms, lowering lock hold
> time) have "automatic" benefits with kernel preemption, though, and that
> has been what I have always advocated.
>
Well, but then without preempt, you *still* need to put cond_rescheds
in non-critical-section code. So cond_resched really does seem to be
the only solution (other than preempt).
I think this is why Ingo found he needed a check in might_sleep to get
really good latency (again, I could be wrong here as I haven't been
really following the progress of that work). But imagine when you
unwind *that* hack into the callers. Yuck.
prev parent reply other threads:[~2004-10-06 2:38 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4136E7EF00073144@mail-3.tiscali.it>
2004-10-06 0:30 ` Cannot enable DMA on SATA drive (SCSI-libsata, VIA SATA) Gianluca Cecchi
2004-10-06 0:54 ` Jeff Garzik
2004-10-06 1:00 ` Preempt? (was Re: Cannot enable DMA on SATA drive (SCSI-libsata, VIA SATA)) Roland Dreier
2004-10-06 1:11 ` Jeff Garzik
2004-10-06 1:28 ` Nick Piggin
2004-10-06 1:32 ` Nick Piggin
2004-10-06 1:40 ` Jeff Garzik
2004-10-06 1:52 ` Robert Love
2004-10-06 1:55 ` Jeff Garzik
2004-10-06 2:02 ` Nick Piggin
2004-10-06 2:07 ` Jeff Garzik
2004-10-06 2:28 ` Nick Piggin
2004-10-06 3:17 ` Andrea Arcangeli
2004-10-06 3:27 ` Jeff Garzik
2004-10-06 3:43 ` Nick Piggin
2004-10-06 3:59 ` Jeff Garzik
2004-10-06 4:05 ` Lee Revell
2004-10-06 4:22 ` Nick Piggin
2004-10-06 15:16 ` Aleksandar Milivojevic
2004-10-06 4:03 ` Andrea Arcangeli
2004-10-06 4:08 ` Jeff Garzik
2004-10-06 4:16 ` Lee Revell
2004-10-06 4:26 ` Nick Piggin
2004-10-06 4:46 ` Andrew Morton
2004-10-06 6:04 ` Jeff Garzik
2004-10-06 6:16 ` Andrew Morton
2004-10-06 13:38 ` Jeff Sipek
2004-10-06 4:12 ` Lee Revell
2004-10-06 3:34 ` Nick Piggin
2004-10-06 2:07 ` Robert Love
2004-10-06 2:30 ` Nick Piggin [this message]
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