Messages in this thread | | | Date | Thu, 7 Mar 2013 11:42:48 -0500 | From | Chris Mason <> | Subject | Re: [PATCH v2 0/4] ipc: reduce ipc lock contention |
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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
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