[ltt-dev] Degression from "fix-x86_64-sysenter-trace-race"

[Mathieu Desnoyers]

* Zhaolei (zhaolei at cn.fujitsu.com) wrote:
> Hello,
> 
> I tested lttng's performance by tbench program in x86_64 platform.
> And I found patch named "fix-x86_64-sysenter-trace-race" makes large
> degression(about 5%).
> Here is test result:
> 
> [----------PATCH----------]                     [TBENCH]
> lttng-kernel-trace-thread-flag-s390		1317.08
> lttng-kernel-trace-thread-flag-sh		1315.61
> lttng-kernel-trace-thread-flag-sparc		1305.02
> lttng-kernel-trace-thread-flag-sparc64		1314.06
> lttng-kernel-trace-thread-flag-um		1316.35
> fix-x86_64-sysenter-trace-race			1250.89
> lttng-kernel-trace-thread-flag-x86		1259.07
> lttng-kernel-trace-thread-flag-xtensa		1252.86
> lttng-kernel-trace-thread-flag-api		1253.35
> lttng-use-kernel-trace-thread-flag-api		1251.9
> stringify-support-commas			1247.11
> 
> And if I remove this patch, degression is not happened:
> [----------PATCH----------]                     [TBENCH]
> lttng-kernel-trace-thread-flag-s390		1307.73
> lttng-kernel-trace-thread-flag-sh		1317.33
> lttng-kernel-trace-thread-flag-sparc		1306.85
> lttng-kernel-trace-thread-flag-sparc64		1303.62
> lttng-kernel-trace-thread-flag-um		1312.08
> lttng-kernel-trace-thread-flag-x86		1308.5
> lttng-kernel-trace-thread-flag-xtensa		1310.77
> lttng-kernel-trace-thread-flag-api		1309.05
> lttng-use-kernel-trace-thread-flag-api		1310.26
> stringify-support-commas			1307.69
> 
> I want to know system's benchmark when lttng turn off,
> so test environment is following:
> - Compile kernel with lttng patch up to given one and default config,
> - Install kernel, Reboot system,
>   (don't load any lttng module, don't run ltt-arm or lttctl)
> - Begin tbench test.
> 
> Plarform is RHEL5.2 root filesystem with linux-2.6.27.7 and lttng-0.60 patchs.
> Hardware is 4 * Intel(R) Xeon(R) X5260 at 3.33GHz with 4G memory.
> 
> I think [fix-x86_64-sysenter-trace-race] should not leads so large degression,
> But I tested several times and result is near.
> 

Hrm, interesting. Can you give your full kernel .config ? I'd like to
see if the _TIF_SYSCALL_AUDIT or _TIF_SECCOMP bits are set.

If you have a better way to support asynchronously changing the thread
flags and still have the affected running threads running correctly, I'm
willing to consider it.

Mathieu

> B.R.
> Zhaolei
> 
> 
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-- 
Mathieu Desnoyers
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