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Date: Tue, 6 Aug 2002 14:47:14 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
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To: Duc Vianney <dvianney@us.ibm.com>
cc: linux-kernel@vger.kernel.org, <lse-tech@lists.sourceforge.net>,
       <mcao@us.ibm.com>, <bhartner@us.ibm.com>
Subject: Re: IPC lock patch performance improvement
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On Mon, 5 Aug 2002, Duc Vianney wrote:
> I ran the LMbench Pipe and IPC latency test bucket against the IPC lock
> patch from Mingming Cao and found the patch improves the performance of
> those functions from 1% to 9%. See the attached data. The kernel under
> test is 2.5.29, SMP kernel running on a 4-way 500 MHz. The data for
> 2.5.29s4-ipc represents the average of three runs.
> 
>                                                            Percent
>                                   2.5.29s4 2.5.29s4-ipc Improvement
> Pipe latency                         12.51     11.43         9%
> AF_Unix sock stream latency          21.61     19.82         8%
> UDP latency using localhost          36.28     35.12         3%
> TCP latency using localhost          56.90     54.89         4%
> RPC/tcp latency using local host    123.30    121.91         1%
> RPC/udp latency using localhost      89.78     88.70         1%
> TCP/IP connection cost to localhost 192.74    187.76         3%
> Note: Latency is in microseconds
> Note: 2.5.29s4 is the base 2.5.29 SMP kernel running on a 4-way,
> 2.5.29s4-ipc is the base 2.5.29 SMP kernel built with IPC lock patch.

Please show me I'm wrong, but so far as I can see (from source and
breakpoints) LMbench never touches the SysV IPC code, which is the only
code affected by Mingming's proposed IPC locking changes.  I believe
LMbench tests InterProcessCommunication via pipes and sockets,
not via the SysV IPC msg sem and shm.

If that's right, then your improvement is magical; but we can
hope for even better when the appropriate codepaths are tested.

Hugh

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