Re: The sample time decreases when I run high cpu utilization job.

Thanks, William and Michael.

I will try later and post the results.

Have a good weekend!

2016-03-11 10:14 GMT-05:00 William Cohen <[email protected]>:

> On 03/10/2016 12:38 PM, Tim Chou wrote:
> > Hi All,
> >
> > I use oprofile to try profile the database server's (MySQL) performance.
> >
> > I start with this command before I start my test:
> > sudo nohup operf --pid `pgrep mysqld` &
> > All the tests will be run for 150s.
> >
> > When the CPU utilization is low, the sample number seems reasonable.
> > However, when the CPU utilization is very high, more than 100%, the
> sample number decreases dramatically.
> >
> > *Because the sample numbers change a lot in these tests. So I'm not sure
> if I can still believe the results I got in the high CPU utilization case.
> I think the sampling should be done in a fix time interval. So the sampling
> number should be similar.*
> >
> > The total sample numbers are 42417612 samples and 1226 samples, for 70%
> CPU utilization and 100% CPU utilization.
> >
> > *Is my understanding right? Or what's the right way to use oprofile in
> the high CPU utilization case?*
> >
> > Looking forward to your reply.
> >
> > Thanks,
> > Tim
>
> Hi Tim,
>
> I suspect that the sampling is being throttled by perf in the kernel and
> that is reducing the number of samples.  Look through the /etc/log/messages
> to see if there are message related to that.
>
> oprofile in this exmaple should be using the default event for example on
> my machine:
>
> $ ophelp -d
> CPU_CLK_UNHALTED:100000:0:1:1
>
> So one sample every 100,000 clock cycles.  For a machine with 2.4GHz clock
> that would be 24,000 samples per processor.
> You might try increasing the sampling interval listed by "ophelp -d"
> something like:
>
> sudo nohup operf -e CPU_CLK_UNHALTED:1000000:0:1:1 -pid `pgrep mysqld`&
>
> See if increasing the interval between samples improves the situation.
>
> -Will
>
> >
> ---------------------------------------------------------------------------------
> > Below are the symbols results.
> > 70% cpu utilization:
> > samples  %        image name               symbol name
> > 2340974   5.5390  mysqld                   MYSQLparse(THD*)
> > 1024614   2.4243  mysqld                   rec_get_offsets_func(unsigned
> char const*, dict_index_t c
> > onst*, unsigned long*, unsigned long, mem_block_info_t**)
> > 610260    1.4439  mysqld                   lex_one_token(YYSTYPE*, THD*)
> [clone .constprop.119]
> >
> >>100% cpu utilization:
> >
> > samples  %        image name               symbol name
> > 63        4.8951  libc-2.22.so <http://libc-2.22.so>
>  __strcmp_sse2_unaligned
> > 60        4.6620  mysqld                   fill_schema_collation(THD*,
> TABLE_LIST*, Item*)
> > 44        3.4188  mysqld                   my_strnncollsp_utf8
> > 29        2.2533  libc-2.22.so <http://libc-2.22.so>
>  __memcpy_avx_unaligned
> >
> >
> >
> >
> ------------------------------------------------------------------------------
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> > Accelerate data analysis in your applications with
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> >
> >
> >
> > _______________________________________________
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> > [email protected]
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> >
>
>
>
> ------------------------------------------------------------------------------
> Transform Data into Opportunity.
> Accelerate data analysis in your applications with
> Intel Data Analytics Acceleration Library.
> Click to learn more.
> http://pubads.g.doubleclick.net/gampad/clk?id=278785111&iu=/4140
> _______________________________________________
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>

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