Re: [PATCH v2 0/4] ipc: reduce ipc lock contention

[Chris Mason <chris.mason@fusionio.com>]

On Thu, Mar 07, 2013 at 08:54:55AM -0700, Dave Kleikamp wrote:
> On 03/07/2013 06:55 AM, Chris Mason wrote:
> > On Thu, Mar 07, 2013 at 01:45:33AM -0700, Peter Zijlstra wrote:
> >> On Tue, 2013-03-05 at 15:53 -0500, Rik van Riel wrote:
> >>
> >>> Indeed.  Though how well my patches will work with Oracle will
> >>> depend a lot on what kind of semctl syscalls they are doing.
> >>>
> >>> Does Oracle typically do one semop per semctl syscall, or does
> >>> it pass in a whole bunch at once?
> >>
> >> https://oss.oracle.com/~mason/sembench.c
> >>
> >> I think Chris wrote that to match a particular pattern of semaphore
> >> operations the database engine in question does. I haven't checked to
> >> see if it triggers the case in point though.
> >>
> >> Also, Chris since left Oracle but maybe he knows who to poke.
> >>
> > 
> > Dave Kleikamp (cc'd) took over my patches and did the most recent
> > benchmarking.  Ported against 3.0:
> > 
> > https://oss.oracle.com/git/?p=linux-uek-2.6.39.git;a=commit;h=c7fa322dd72b08450a440ef800124705a1fa148c
> > 
> > The current versions are still in the 2.6.32 oracle kernel, but it looks
> > like they reverted this 3.0 commit.  I think with Manfred's upstream
> > work my more complex approach wasn't required anymore, but hopefully
> > Dave can fill in details.
> 
> From what I recall, I could never get better performance from your
> patches that we saw with Manfred's work alone. I can't remember the
> reasons for including and then reverting the patches from the 3.0
> (2.6.39) Oracle kernel, but in the end we weren't able to justify their
> inclusion.

Ok, so after this commit, oracle was happy:

commit fd5db42254518fbf241dc454e918598fbe494fa2
Author: Manfred Spraul <manfred@colorfullife.com>
Date:   Wed May 26 14:43:40 2010 -0700

    ipc/sem.c: optimize update_queue() for bulk wakeup calls

But that doesn't explain why Davidlohr saw semtimedop at the top of the
oracle profiles in his runs.

Looking through the patches in this thread, I don't see anything that
I'd expect to slow down oracle TPC numbers.

I dealt with the ipc_perm lock a little differently:

https://oss.oracle.com/git/?p=linux-uek-2.6.39.git;a=commitdiff;h=78fe45325c8e2e3f4b6ebb1ee15b6c2e8af5ddb1;hp=8102e1ff9d667661b581209323faaf7a84f0f528

My code switched the ipc_rcu_hdr refcount to an atomic, which changed
where I needed the spinlock.  It may make things easier in patches 3/4
and 4/4.

(some of this code was Jens, but at the time he made me promise to
pretend he never touched it)

-chris