Re: cli/sti vs local_cmpxchg and local_add_return

Josh Boyer
2009-03-18T11:57:11Z

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@localhost ~]$