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Date: Mon, 30 Oct 2000 09:26:59 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: mingo@elte.hu
To: Andi Kleen <ak@suse.de>
Cc: "Jeff V. Merkey" <jmerkey@vger.timpanogas.org>,
        linux-kernel@vger.kernel.org
Subject: Re: 2.2.18Pre Lan Performance Rocks!
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On Mon, 30 Oct 2000, Andi Kleen wrote:

> One problem in Linux 2.2 is that kernel threads reload their VM on
> context switch (that would include the nfsd thread), this should be
> fixed in 2.4 with lazy mm. Hmm actually it should be only fixed for
> true kernel threads that have been started with kernel_thread(), the
> "pseudo kernel threads" like nfsd uses probably do not get that
> optimization because they don't set their MM to init_mm.

yes, but for this there is an explicit mechanizm to lazy-MM during lengthy
system calls, an example is in buffer.c:

                user_mm = start_lazy_tlb();
                error = sync_old_buffers();
                end_lazy_tlb(user_mm);

> > to get disproportiantely higher in Linux than NetWare 5.x and when it hits
> > 60% of total clock cycles, Linux starts dropping off.  NetWare 5.x is 1/8 
> 
> I think that can be explained by the copying.

yes. Constant copying contaminates the L1/L2 caches and creates dirty
cachelines all around the place. Fixed in 2.4 + TUX ;-)

	Ingo

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