Re: vmalloc performance

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, Apr 19, 2010 at 9:58 PM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> Hi,
>
> On Mon, 2010-04-19 at 00:14 +0900, Minchan Kim wrote:
>> On Fri, 2010-04-16 at 15:10 +0100, Steven Whitehouse wrote:
>> > Hi,
>> >
>> > On Fri, 2010-04-16 at 01:51 +0900, Minchan Kim wrote:
>> > [snip]
>> > > Thanks for the explanation. It seems to be real issue.
>> > >
>> > > I tested to see effect with flush during rb tree search.
>> > >
>> > > Before I applied your patch, the time is 50300661 us.
>> > > After your patch, 11569357 us.
>> > > After my debug patch, 6104875 us.
>> > >
>> > > I tested it as changing threshold value.
>> > >
>> > > threshold time
>> > > 1000              13892809
>> > > 500               9062110
>> > > 200               6714172
>> > > 100               6104875
>> > > 50                6758316
>> > >
>> > My results show:
>> >
>> > threshold        time
>> > 100000           139309948
>> > 1000             13555878
>> > 500              10069801
>> > 200              7813667
>> > 100              18523172
>> > 50               18546256
>> >
>> > > And perf shows smp_call_function is very low percentage.
>> > >
>> > > In my cases, 100 is best.
>> > >
>> > Looks like 200 for me.
>> >
>> > I think you meant to use the non _minmax version of proc_dointvec too?
>>
>> Yes. My fault :)
>>
>> > Although it doesn't make any difference for this basic test.
>> >
>> > The original reporter also has 8 cpu cores I've discovered. In his case
>> > divided by 4 cpus where as mine are divided by 2 cpus, but I think that
>> > makes no real difference in this case.
>> >
>> > I'll try and get some further test results ready shortly. Many thanks
>> > for all your efforts in tracking this down,
>> >
>> > Steve.
>>
>> I voted "free area cache".
> My results with this patch are:
>
> vmalloc took 5419238 us
> vmalloc took 5432874 us
> vmalloc took 5425568 us
> vmalloc took 5423867 us
>
> So thats about a third of the time it took with my original patch, so
> very much going in the right direction :-)

Good. :)

>
> I did get a compile warning:
>  CC      mm/vmalloc.o
> mm/vmalloc.c: In function ‘__free_vmap_area’:
> mm/vmalloc.c:454: warning: unused variable ‘prev’
>
> ....harmless, but it should be fixed before the final version,

Of course. It's not formal patch but for showing concept  . :)

Thanks for consuming precious your time. :)
As Nick comments, I have to do further work.
Maybe Nick could do it faster than me.
Anyway, I hope it can solve your problem.

Thanks, Steven.

>
> Steve.
>
>
>



-- 
Kind regards,
Minchan Kim

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