Re: find_vma() cachehit rate

[Nick Piggin <nickpiggin@yahoo.com.au>]

Michael Buesch wrote:
> Hi,
> 
> I just saw this comment in find_vma():
>   /* Check the cache first. */
>   /* (Cache hit rate is typically around 35%.) */
> 
> I just wanted to play around a bit. Just for fun.
> So I wrote the attached patch to collect find_vma()
> statistics. I was wondering why my cache hit rate is around
> 60%. It's always between 55 and 65 percent. Depending on
> the workload.
> Is this on obsolete comment from the 2.4 days, maybe?
> 
> mb@lfs:~$ cat /proc/findvma_stat 
> findvma_stat_cachehit  == 356524
> findvma_stat_cachemiss == 248728
> findvma_stat_fail      == 0
> cachehit percentage    == 58%
> cachemiss percentage   == 41%
> fail percentage        == 0%
> 
> My kernel is:
> mb@lfs:~$ uname -r
> 2.6.10-rc2-ck2-nozeroram-findvmastat
> 
> If you are interrested to comment on this, please CC: me,
> as I'm not subscribed to this mailing list. Thanks.
> 

I think the cache hit rate will be pretty variable depending on the
workload. For example, anything making use of threads, especially on
an SMP system has the potential to decrease the cache's performance.

I wouldn't worry too much about the comment - it isn't really
misleading, at worst inaccurate in a harmless sort of way. Basically
it is there to say "hey, this really does help", I guess.
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