From: Jeff Garzik <jgarzik@pobox.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrea Arcangeli <andrea@novell.com>,
Robert Love <rml@novell.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: Tue, 05 Oct 2004 23:59:07 -0400 [thread overview]
Message-ID: <41636D8B.8020401@pobox.com> (raw)
In-Reply-To: <416369F9.7050205@yahoo.com.au>
Nick Piggin wrote:
> Jeff Garzik wrote:
>
>> Andrea Arcangeli wrote:
>>
>>> So I disagree with your claim that preempt risks to hide inefficient
>>> code, there are many other (probably easier) ways to detect inefficient
>>> code than to check the latencies.
>>
>>
>>
>>
>> You're ignoring the argument :)
>>
>> If users and developers are presented with the _impression_ that long
>> latency code paths don't exist, then nobody is motivated to profile
>> them (with any tool), much less fix them.
>>
>
> But even without preempt you'd still have to profile the latency.
You're making my point for me. If the bandaid (preempt) is not active,
then the system can be accurated profiled. If preempt is active, then
it is potentially hiding trouble spots.
The moral of the story is not to use preempt, as it
* potentially hides long latency code paths
* potentially introduces bugs, as we've seen with net stack and many
other pieces of code
* is simply not needed, if all code paths are fixed
Jeff
next prev parent reply other threads:[~2004-10-06 3:59 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 [this message]
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
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