lkml.org 
[lkml]   [2007]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex

* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> I was toying with a scalable rw_mutex and found that it gives ~10%
> reduction in system time on ebizzy runs (without the MADV_FREE patch).
>
> 2-way x86_64 pentium D box:
>
> 2.6.21
>
> /usr/bin/time ./ebizzy -m -P
> 59.49user 137.74system 1:49.22elapsed 180%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+33555877minor)pagefaults 0swaps
>
> 2.6.21-rw_mutex
>
> /usr/bin/time ./ebizzy -m -P
> 57.85user 124.30system 1:42.99elapsed 176%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+33555877minor)pagefaults 0swaps

nice! This 6% runtime reduction on a 2-way box will i suspect get
exponentially better on systems with more CPUs/cores.

i also like the design, alot: instead of doing a full new lock type
(with per-arch changes, extra lockdep support, etc. etc) you layered the
new abstraction ontop of mutexes. This makes this hard locking
abstraction look really, really simple, while the percpu_counter trick
makes it scale _perfectly_ for the reader case. Congratulations!

given how nice this looks already, have you considered completely
replacing rwsems with this? I suspect you could test the correctness of
that without doing a mass API changeover, by embedding struct rw_mutex
in struct rwsem and implementing kernel/rwsem.c's API that way. (the
real patch would just flip it all over to rw-mutexes)

Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-05-11 18:03    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site