lkml.org 
[lkml]   [2009]   [Jan]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: lmbench lat_mmap slowdown with CONFIG_PARAVIRT

    * Ingo Molnar <mingo@elte.hu> wrote:

    > -----------------------------------------------
    > | Performance counter stats for './mmap-perf' |
    > -----------------------------------------------
    > | |
    > | x86-defconfig | PARAVIRT=y
    > |------------------------------------------------------------------
    > |
    > | 1311.554526 | 1360.624932 task clock ticks (msecs) +3.74%
    > | |
    > | 1 | 1 CPU migrations
    > | 91 | 79 context switches
    > | 55945 | 55943 pagefaults
    > | ............................................
    > | 3781392474 | 3918777174 CPU cycles +3.63%
    > | 1957153827 | 2161280486 instructions +10.43%
    > | 50234816 | 51303520 cache references +2.12%
    > | 5428258 | 5583728 cache misses +2.86%
    > | |
    > | 1314.782469 | 1363.694447 time elapsed (msecs) +3.72%
    > | |
    > -----------------------------------
    >
    > The most surprising element is that in the paravirt_ops case we run 204
    > million more instructions - out of the ~2000 million instructions total.

    So because this test does exactly 1 million MM syscalls, the average is
    easy to calculate:

    The native kernel's average MM syscall cost is 1957 instructions - with
    CONFIG_PARAVIRT=y that increases by +10.43% to 2161 instructions. There's
    over 200 extra instructions executed per MM syscall that we only do due to
    CONFIG_PARAVIRT=y.

    Ingo


    \
     
     \ /
      Last update: 2009-01-20 20:39    [W:2.931 / U:0.176 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site