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

[Rik van Riel]

On 03/05/2013 03:52 PM, Linus Torvalds wrote:
> On Tue, Mar 5, 2013 at 11:42 AM, Waiman Long <Waiman.Long@xxxxxx> wrote:
> > The recommended kernel.sem value from Oracle is "250 32000 100 128". I have
> > tried to reduce the maximum semaphores per array (1st value) while
> > increasing the max number of arrays. That tends to reduce the ipc_lock
> > contention in kernel, but it is against Oracle's recommendation.
>
> Ok, the Oracle recommendations seem to be assuming that we'd be
> scaling the semaphore locking sanely, which we don't. Since we share
> one single lock for all semaphores in the whole array, Oracle's
> recommendation does the wrong thing for our ipc_lock contention.

> David's patch should make it much easier to do the locking more
> fine-grained, and it sounds like Rik is actively working on that,

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?

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