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xen-devel
Re: [Xen-devel] MPI benchmark performance gap between native linux anddo
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To: |
"Santos, Jose Renato G (Jose Renato Santos)" <joserenato.santos@xxxxxx> |
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Subject: |
Re: [Xen-devel] MPI benchmark performance gap between native linux anddomU |
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From: |
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> |
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Date: |
Tue, 5 Apr 2005 09:59:12 +0100 |
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Cc: |
"Turner, Yoshio" <yoshio_turner@xxxxxx>, Xen-devel@xxxxxxxxxxxxxxxxxxx, Aravind Menon <aravind.menon@xxxxxxx>, xuehai zhang <hai@xxxxxxxxxxxxxxx>, G John Janakiraman <john@xxxxxxxxxxxxxxxxxxx> |
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Tue, 05 Apr 2005 08:56:03 +0000 |
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On 5 Apr 2005, at 03:07, Santos, Jose Renato G (Jose Renato Santos)
wrote:
Here is a brief explanation of the problem we found and the solution
that worked for us.
Xenolinux allocates a full page (4KB) to store socket buffers instead
of using just MTU bytes as in traditional linux. This is necessary to
enable page exchanges between the guest and the I/O domains. The side
effect of this is that memory space used for socket buffers is not
very
efficient.
This is true, but these days we lie to the network stack about how big
the skb data area is. The 'truesize' field, which is what I think is
used for socket buffer accounting, will be around 1600 bytes, not 4096.
So I would expect the old trick of reducing the receive windows not to
work: but if it does then that is very interesting!
-- Keir
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