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Date: Tue, 1 Oct 2002 11:03:05 +0530
From: Dipankar Sarma <dipankar@in.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: george anzinger <george@mvista.com>,
       Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org,
       William Lee Irwin III <wli@holomorphy.com>,
       Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
       "David S. Miller" <davem@redhat.com>
Subject: Re: [patch] smptimers, old BH removal, tq-cleanup, 2.5.39
Message-ID: <20021001110305.B693@in.ibm.com>
Reply-To: dipankar@in.ibm.com
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On Tue, Oct 01, 2002 at 05:51:45AM +0200, Ingo Molnar wrote:
> the smp_processor_id()/(HZ*num_cpus) 'interleaving' of every APIC clock
> was an SMP scalability issue, and it was done as part of the smptimers
> patch. It just got into the kernel much earlier.
> 
> but these days, with the removal of BHs, it might be less of a factor,
> mainly because timers have no global synchronization anymore, so we can
> again try to not interleave the APIC clocks. Only testing will tell,
> because there might be some interaction between timer-generated code
> still.

Yes, with earlier versions of smptimers where global_bh_lock was
still being acquired to serialize with BHs, local timer clocks needed
to be spaced over a HZ to reduce contention. Archs that didn't space
the clocks perfromed poorly with smptimers as Anton found out with
ppc64 and had to change.

> 
> Dipankar, wli, would it be possible to try the attached simple patch with
> some of the more complex networking loads? The patch gets rid of the APIC
> timer interleaving.

I will give it a spin.

Thanks
-- 
Dipankar Sarma  <dipankar@in.ibm.com> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.
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