On 1/22/13 5:50 PM, Jan Kara wrote:

On Mon 21-01-13 18:11:30, Ted Tso wrote:

quoted

On Tue, Jan 22, 2013 at 12:04:32AM +0100, Sedat Dilek wrote:

quoted

Beyond the FUSE/LOOP fun, will you apply this patch to your linux-next GIT tree?

Feel free to add...

     Tested-by: Sedat Dilek [off-list ref]

A similiar patch for JBD went through your tree into mainline (see [1] and [2]).

I'm not at all convinced that this patch has anything to do with your
problem.  I don't see how it could affect things, and I believe you
mentioned that you saw the problem even with this patch applied?  (I'm
not sure; some of your messages which you sent were hard to
understand, and you mentioned something about trying to send messages
when low on sleep :-).

In any case, the reason why I haven't pulled this patch into the ext4
tree is because I was waiting for Eric and some of the performance
team folks at Red Hat to supply some additional information about why
this commit was making a difference in performance for a particular
proprietary, closed source benchmark.

  Just a small correction - it was aim7 AFAIK which isn't closed source
(anymore). You can download it from SourceForge
(http://sourceforge.net/projects/aimbench/files/aim-suite7/Initial%20release/).
Now I have some reservations about what the benchmark does but historically
it has found quite a few issues for us as well.

quoted

I'm very suspicious about applying patches under the "cargo cult"
school of programming.  ("We don't understand why it makes a
difference, but it seems to be good, so bombs away!" :-)

  Well, neither am I ;) But it is obvious the patch speeds up
log_start_commit() by 'a bit' (taking spinlock, disabling irqs, ...). And
apparently 'a bit' is noticeable for particular workload on a particular
machine - commit statistics Eric provided showed that clearly. I'd still be
happier if Eric also told us how much log_start_commit() calls there were
so that one could verify that 'a bit' could indeed multiply to a measurable
difference. But given how simple the patch is, I gave away after a while
and just merged it...

I am still trying to get our perf guys to collect that data, FWIW...
I will send it when I get it.  I bugged them again today.  :)

(Just to be sure: I was going to measure the wakeups the old way, and the
avoided wakeups with the new change; sound ok?)

-Eric

								Honza