Re: Regression seen for patch "sched:dont decrease idle sleepavg"
From: Martin Bligh
Date: Mon May 08 2006 - 21:07:02 EST
Con Kolivas wrote:
Tim Chen writes:
Con,
As a result of the patch "sched:dont decrease idle sleep avg"
introduced after 2.6.15, there is a 4% drop in Volanomark throughput
on our Itanium test machine. Probably the following happened:
Compared to previous code, this patch slightly increases the the
priority boost when a job is woken up.
This adds priority spread and variations to the wait time of jobs
on run queue if we have a lot of similar jobs in the system.
See patch:
http://www.kernel.org/git/?
p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e72ff0bb2c163eb13014ba113701bd42dab382fe
Lovely
This patch corrects a bug in the original code which unintentionally
dropped the priority of tasks that were idle but were already high
priority on other merits. It doesn't further increase the priority. The
4% almost certainly is due to the lack of any locking in the threading
model used by the java virtual machine on volanomark and it being pure
luck that penalising particularly idle tasks previously improved the
wakeup timing of basically yielding dependant threads. This patch did
fix bugs related to interactive yet idle tasks like consoles
misbehaving. The fact that the presence of that particular bug improved
a multithreaded benchmark that uses such a threading model is pure
chance and (obviously) not design. I wouldn't like to see this bug
reintroduced on the basis of this benchmark result.
Volanomark (and most Java benchmarks) are random number generators
anyway, especially when it comes to scheduler patches. They're doing
such utterly stupid things anyway that I don't think we should care
if we break them ...
M.
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