Re: Poor thread performance on Linux vs. Solaris

On Monday 08 September 2003 2:48 pm, Perez-Gonzalez, Inaky wrote:

> It'd be interesting to verify if there is still a lot of contention in
> the locking.

oprofile results on 2.6.0-0.test4.1.32 with Boris' futex_q_lock patch:

c011e410 1149     0.923136    try_to_wake_up
c011f250 1280     1.02839     schedule
c014c5e0 1314     1.0557      __attach_vcache
c0116cb0 1392     1.11837     mark_offset_tsc
c010af6b 2181     1.75227     sysenter_past_esp
c0150300 3164     2.54204     follow_page
c014b6b0 3529     2.83529     mark_page_accessed
c0147b60 3540     2.84413     poison_obj
c011e270 4046     3.25066     kunmap_atomic
c0147bf0 4628     3.71825     scan_poisoned_obj
c011e1e0 4955     3.98097     kmap_atomic
c0138100 24115    19.3746     do_futex
c0138bcd 46827    37.622      .text.lock.futex

> A question about your app: are there many different locks used at the
> same time or the number is actually low?

Many.  I'd estimate at least 15 on the typical code path (which I'm 
exercising with the performance test).  However, I'm not the original 
architect so I'm not certain, but it definitely isn't  a low number like 
2 or 3.

> No matter how we do it, there is still a bunch of lock acquisition in
> the futex code that would serialize access [specially if they are locks
> within the same thread, like current->mm->page_table_lock].
>
> And then we also have vcache_lock--this one is also serializing
> everything, as it is taken unconditionally whenever we call
> lock_futex_mm().

Oh! Hits in .text.lock.futex represent spinning for any of the locks 
acquired in futex.c, yes?  Originally I thought it represented time spent 
spinning while waiting for the 'futex' lock in 'futex.c'.  But's that's 
obviously gone after Boris' patch.

Now - how to distinguish between these locks in the oprofile results?  Can 
I add a few helper files that just contain functions to acquire/release 
one lock (assuming one .text.lock section is created per file)?  For 
instance, futex_vcache_lock.c, futex_page_table_lock.c, etc?

Bill


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