Date: Fri, 19 Mar 2004 20:14:50 -0800
From: Andrew Morton <akpm@osdl.org>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: markw@osdl.org, axboe@suse.de, linux-kernel@vger.kernel.org
Subject: Re: 2.6.4-mm2
Message-Id: <20040319201450.5da6847a.akpm@osdl.org>
In-Reply-To: <405BC003.6080507@cyberone.com.au>
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Nick Piggin <piggin@cyberone.com.au> wrote:
>
>  >>>
>  >>Thanks, so it's the CPU scheduler changes.  Is that machine hyperthreaded? 
>  >>And do you have CONFIG_X86_HT enabled?
>  >>
>  >
>  >Yes and CONFIG_X86_HT is enabled but I have hyperthreading disabled with
>  >'acpi=off noht' (whichever one does it.)  
>  >
> 
> 
>  The oprofile for the 01 kernel says
>  CPU: P4 / Xeon, speed 1497.76 MHz (estimated)
>  while the 02 kernel says
>  CPU: P4 / Xeon with 2 hyper-threads, speed 1497.57 MHz (estimated)
>  What's going on there?

Does the sched-domains patch break `acpi=off' or `noht'?

>  Other than that, nothing in the kernel profile jumps out at me:
>  schedule, __copy_from_user_ll and __copy_to_user_ll are all
>  significantly lower *after* the CPU scheduler changes, which
>  is an indicator that cache behaviour is better.

No, it indicates that the kernel is getting less work done.

>  Sar says average context switches/second were 9064 and  6567 before
>  and after.
> 
>  The only thing I can see is the CPU utilisation averages show the
>  scheduler patches have more of a tendancy to load up one CPU more
>  before moving to another. This actually should be good behaviour,
>  generally but I wonder if it is hurting at all. I would be really
>  surprised if it was that significant.

This machine is I/O-bound, the CPUs are mostly idle.  It would appear to be
some interaction between the I/O system and the CPU scheduler.  Haven't we
seen that with reaim also?

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