Message-ID: <41EE5601.7060700@yahoo.com.au>
Date: Wed, 19 Jan 2005 23:43:45 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: davidm@hpl.hp.com
CC: Linus Torvalds <torvalds@osdl.org>, "Luck, Tony" <tony.luck@intel.com>,
       linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: pipe performance regression on ia64
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David Mosberger wrote:
>>>>>>On Wed, 19 Jan 2005 10:34:30 +1100, Nick Piggin <nickpiggin@yahoo.com.au> said:
> 
> 
>   Nick> David I remember you reporting a pipe bandwidth regression,
>   Nick> and I had a patch for it, but that hurt other workloads, so I
>   Nick> don't think we ever really got anywhere. I've recently begun
>   Nick> having another look at the multiprocessor balancer, so
>   Nick> hopefully I can get a bit further with it this time.
> 
> While it may be worthwhile to improve the scheduler, it's clear that
> there isn't going to be a trivial "fix" for this issue, especially
> since it's not even clear that anything is really broken.  Independent
> of the scheduler work, it would be very useful to have a pipe
> benchmark which at least made the dependencies on the scheduler
> obvious.  So I think improving the scheduler and improving the LMbench
> pipe benchmark are entirely complementary.
> 

Oh that's quite true. A bad score on SMP on the pipe benchmark does
not mean anything is broken.

And IMO, probably many (most?) lmbench tests should be run with all
processes bound to the same CPU on SMP systems to get the best
repeatability and an indication of the basic serial speed of the
operation (which AFAIK is what they aim to measure).

Having the scheduler take care of process placement is interesting
too, of course. But it adds a new variable to the tests, which IMO
doesn't always suit lmbench too well.

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