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Date: Mon, 29 Jul 2002 22:38:40 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Andrew Theurer <habanero@us.ibm.com>, linux-kernel@vger.kernel.org,
       Marcelo Tosatti <marcelo@conectiva.com.br>
Subject: Re: Linux 2.4.19-rc3 (hyperthreading)
Message-ID: <20020729203840.GA1201@dualathlon.random>
References: <200207291454.30076.habanero@us.ibm.com> <1027978122.4050.22.camel@irongate.swansea.linux.org.uk>
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On Mon, Jul 29, 2002 at 10:28:42PM +0100, Alan Cox wrote:
> On Mon, 2002-07-29 at 20:54, Andrew Theurer wrote:
> > I would caution against having hyperthreading on by default in the 2.4.19 
> > release.  I am seeing a significant degrade in network workloads on P4 with 
> > hyperthreading on.  On 2.4.19-pre10, I get 788 Mbps on NetBench, but on 
> > 2.4.19-rc1 (and probably rc3, should know in an hour), I get 690 Mbps.  It is 
> > clearly a hyperthreading/interrupt routing issue.  On this system (4 x P4), 
> 
> Quite possibly. I've just merged the O(1) scheduler load balancing fixes
> for the hyperthreading stuff, rc3 uses the old scheduler so that isnt

btw, please make sure to merge my patch, the original one had several
severe bugs.

> Its quite possible the irq routing ought to be smarter, at the moment
> I'm not sure of the best approaches.

fixing irq routing is even simpler, should be a three liner, I heard
somebody used kernel threads for it, that's certainly not needed
(btw, also for the irq routing I recommend you to merge my modified
version, the original one looked more to make P4 SMP look like a PIII
in /proc/interrupts not really to improve performance, performance
improves only if the irq stops trashing around and if it stops
overwriting the ioapic registers even if there's no routing change
required).

Andrea
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