linux-kernel - Does the scheduler know about the cache topology?

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Message-ID: <20110207095141.GA26132@andariel.informatik.uni-erlangen.de>
Date:	Mon, 7 Feb 2011 10:51:42 +0100
From:	Daniel Tiron <dtiron@...ian.armed.us>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: Does the scheduler know about the cache topology?

Hi all.

I did some performance tests on a Core 2 Quad machine [1] with QEMU.
A QEMU instance creates one main thread and one thread for each virtual
CPU. There were two vms with one CPU each, which make four threads.

I tried different combinations where I pinned one tgread to one physical
core with taskset and measured the network performance between the vms
with iperf [2]. The best result was achieved with each vm (main and CPU
thread) assigned to one cache group (core 0 & 1 and 2 & 3).

But it also turns out that letting the scheduler handle the assignment
works well, too: The results where no pinning was done were just
slightly below the best. So I was wondering, is the Linux scheduler
aware of the CPU's cache topology?

I'm curious to hear your opinion.

Thanks,
Daniel

[1] Core 0 and 1 share one L2 cache and so do 2 and 3
[2] The topic of my research is networking performance. My interest in
    cache awareness is only a side effect.

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