Re: [PATCH 1/4] omap: mailbox cleanup: convert rwlocks to spinlock

[Ohad Ben-Cohen <ohad@wizery.com>]

Hi Hiroshi,

On Wed, Apr 28, 2010 at 10:50 AM, Hiroshi DOYU <Hiroshi.DOYU@nokia.com> wrote:
> Hi Ohad,
>
> From: ext Ohad Ben-Cohen <ohad@wizery.com>
> Subject: [PATCH 1/4] omap: mailbox cleanup: convert rwlocks to spinlock
> Date: Tue, 27 Apr 2010 19:56:19 +0200
>
>> rwlocks are slower and have potential starvation issues so spinlocks are
>> generally preferred
>
> Would it be possible to explain the above a bit more?

Sure, sorry for the laconic description.

Jonathan Corbet wrote a nice summary about this:
http://lwn.net/Articles/364583/

We could switch to rcu, but it's really an overkill because we don't really
have a high bandwidth of readers (omap_mbox_get is not being called
so much).

The only disadvantage of a plain spinlock is that readers now will have
to wait in the line, but since omap_mbox_get isn't called so frequently,
I guess that by moving to spinlocks the average performance will actually
increase (since spinlocks are faster and most likely there will not be
multiple concurrent calls to omap_mbox_get).

Anyway I only consider this as a cleanup and not really a performance
issue, as mboxes_lock is not really on a hot path.

Thanks,
Ohad.


>