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

[Zhaolei]

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.

B.R.
Zhaolei