linux-kernel - Re: cli/sti vs local_cmpxchg and local_add

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Message-ID: <20090318115624.GF3873@zod.rchland.ibm.com>
Date:	Wed, 18 Mar 2009 07:56:24 -0400
From:	Josh Boyer <jwboyer@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	ltt-dev@...ts.casi.polymtl.ca
Subject: Re: cli/sti vs local_cmpxchg and local_add_return

On Mon, Mar 16, 2009 at 09:32:20PM -0400, Mathieu Desnoyers wrote:
>Hi,
>
>I am trying to get access to some non-x86 hardware to run some atomic
>primitive benchmarks for a paper on LTTng I am preparing. That should be
>useful to argue about performance benefit of per-cpu atomic operations
>vs interrupt disabling. I would like to run the following benchmark
>module on CONFIG_SMP :
>
>- PowerPC
>- MIPS
>- ia64
>- alpha
>
>usage :
>make
>insmod test-cmpxchg-nolock.ko
>insmod: error inserting 'test-cmpxchg-nolock.ko': -1 Resource temporarily unavailable
>dmesg (see dmesg output)
>
>If some of you would be kind enough to run my test module provided below
>and provide the results of these tests on a recent kernel (2.6.26~2.6.29
>should be good) along with their cpuinfo, I would greatly appreciate.
>
>Here are the CAS results for various Intel-based architectures :
>
>Architecture         | Speedup                      |      CAS     |         Interrupts         |
>                     | (cli + sti) / local cmpxchg  | local | sync | Enable (sti) | Disable (cli)
>-------------------------------------------------------------------------------------------------
>Intel Pentium 4      | 5.24                         |  25   | 81   | 70           | 61          |
>AMD Athlon(tm)64 X2  | 4.57                         |  7    | 17   | 17           | 15          |
>Intel Core2          | 6.33                         |  6    | 30   | 20           | 18          |
>Intel Xeon E5405     | 5.25                         |  8    | 24   | 20           | 22          |


I know you have results from a POWER6 machine already, but
here are the results on a dual-G5 running 2.6.29-rc7-git4.

If you are interested, I could get you results from running
this on an embedded PowerPC board.

josh

test init
test results: time for baseline
number of loops: 20000
total time: 1532
-> baseline takes 0 cycles
test end
test results: time for locked cmpxchg
number of loops: 20000
total time: 48052
-> locked cmpxchg takes 2 cycles
test end
test results: time for non locked cmpxchg
number of loops: 20000
total time: 29141
-> non locked cmpxchg takes 1 cycles
test end
test results: time for locked add return
number of loops: 20000
total time: 44985
-> locked add return takes 2 cycles
test end
test results: time for non locked add return
number of loops: 20000
total time: 32400
-> non locked add return takes 1 cycles
test end
test results: time for enabling interrupts (STI)
number of loops: 20000
total time: 65579
-> enabling interrupts (STI) takes 3 cycles
test end
test results: time for disabling interrupts (CLI)
number of loops: 20000
total time: 29135
-> disabling interrupts (CLI) takes 1 cycles
test end
test results: time for disabling/enabling interrupts (STI/CLI)
number of loops: 20000
total time: 173594
-> enabling/disabling interrupts (STI/CLI) takes 8 cycles
test end
[jwboyer@...alhost ~]$
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