From: jak@rudolph.ccur.com (Joe Korty)
To: mingo@elte.hu
Cc: joe.korty@ccur.com (Joe Korty),
alan@lxorguk.ukuu.org.uk (Alan Cox),
marcelo@conectiva.com.br (Marcelo Tosatti),
torvalds@transmeta.com (Linus Torvalds),
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.4.18 scheduler bugs
Date: Fri, 15 Mar 2002 17:14:20 -0500 (EST) [thread overview]
Message-ID: <200203152214.WAA27958@rudolph.ccur.com> (raw)
In-Reply-To: <Pine.LNX.4.44.0203152156270.23324-100000@elte.hu> from "Ingo Molnar" at Mar 15, 2002 09:57:06 PM
>>> but even in the Athlon case an IPI is still an IRQ entry, which will add
>>> at least 200 cycles or more to the idle wakeup latency.
>>
>> It is an idle cpu that is spending those 200 cycles.
>
> wrong. When it's woken up it's *not* an idle CPU anymore, and it's the
> freshly woken up task that is going to execute 200 cycles later...
I have to disagree. It is the woken up task *running on the
otherwise idle CPU* that burns up 200 cycles at the tail.
A cpu is wasting, say, 5,000,000 cycles (1GHz/100/2, or 1/2 tick) in
hlt when it could have been doing work. Why worry about an
alternative wakeup path that burns up 200-400 cycles of that on the
otherwise idling cpu, even if it is at the tail.
Joe
next prev parent reply other threads:[~2002-03-15 22:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-15 20:54 Joe Korty
2002-03-15 19:55 ` Ingo Molnar
2002-03-15 21:25 ` Joe Korty
2002-03-15 20:35 ` Ingo Molnar
2002-03-15 21:58 ` Alan Cox
2002-03-15 20:42 ` Ingo Molnar
2002-03-15 21:59 ` Joe Korty
2002-03-15 20:57 ` Ingo Molnar
2002-03-15 22:14 ` Joe Korty [this message]
2002-03-15 23:50 ` Mike Kravetz
2002-03-16 9:23 ` Ingo Molnar
2002-03-15 21:39 ` Alan Cox
2002-03-15 21:26 ` Joe Korty
2002-03-19 2:08 ` Rob Landley
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