[lttng-dev] UST performance

[zhenyu.ren]

Hi,dev    About a month ago,I asked a question about how to do time recording for ust event when vdso_clock_gettime not availble on my platform（Glibc too old）.Recently I implemented a lib to analyze vdso in memory and lookuped the symbol vdso_clock_gettime successfully.With this vdso_clock_gettime availble,I get a 16% improvement in time spending per ust event. I.E. I measured the time taked by a event with 10 bytes string : no   vdso_clock_gettime : 0.642us with vdso_clock_gettime：0.554usHowever，Both the numbers are much higher than the following 0.28us(But closed to 0.5us --W/O opt). So what's the difference between UST(0.28us) and UST W/O OPT(0.5us)?? PS:My hardware2 x Xeon E5-2430  2.20GHz 100MHz FSB (24 cores) 94.6GB / 96GB 1333MHz DDR3 == 6 x 16GB, 6 x emptyThankszhenyu.ren

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