lmbench ctxsw regression with CFS

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To: Ingo Molnar <mingo@...>, Linus Torvalds <torvalds@...>
Cc: Andrew Morton <akpm@...>, Linux Kernel Mailing List <linux-kernel@...>
Date: Wednesday, August 1, 2007 - 10:15 pm

Hi,

I didn't follow all of the scheduler debates and flamewars, so apologies
if this was already covered. Anyway.

lmbench 3 lat_ctx context switching time with 2 processes bound to a
single core increases by between 25%-35% on my Core2 system (didn't do
enough runs to get more significance, but it is around 30%). The problem
bisected to the main CFS commit.

I was really hoping that a smaller runqueue data structure could actually
increase performance with the common case of small numbers of tasks :(

I assume this was a known issue before CFS was merged. Do you know what is
causing the slowdown? Any plans to fix it?

Thanks,
Nick
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Messages in current thread:
lmbench ctxsw regression with CFS, Nick Piggin, (Wed Aug 1, 10:15 pm)
Re: lmbench ctxsw regression with CFS, Linus Torvalds, (Wed Aug 1, 10:31 pm)
Re: lmbench ctxsw regression with CFS, Nick Piggin, (Wed Aug 1, 10:41 pm)
Re: lmbench ctxsw regression with CFS, Ingo Molnar, (Thu Aug 2, 3:19 am)
Re: lmbench ctxsw regression with CFS, Nick Piggin, (Thu Aug 2, 3:31 am)
Re: lmbench ctxsw regression with CFS, Ingo Molnar, (Thu Aug 2, 11:44 am)
Re: lmbench ctxsw regression with CFS, Nick Piggin, (Thu Aug 2, 8:14 pm)
Re: lmbench ctxsw regression with CFS, Ingo Molnar, (Sat Aug 4, 2:50 am)
Re: lmbench ctxsw regression with CFS, Nick Piggin, (Sun Aug 5, 11:29 pm)
Re: lmbench ctxsw regression with CFS, Jens Axboe, (Mon Aug 13, 8:30 am)
Re: lmbench ctxsw regression with CFS, Andrew Morton, (Mon Aug 13, 11:00 pm)
Re: lmbench ctxsw regression with CFS, David Miller, (Mon Aug 13, 11:25 pm)
Re: lmbench ctxsw regression with CFS, Nick Piggin, (Mon Aug 13, 11:23 pm)
Re: lmbench ctxsw regression with CFS, Siddha, Suresh B, (Thu Aug 16, 5:28 pm)