Re: [patch 0/4] ide: Break ide_lock to per-hwgroup lock

[Ravikiran G Thirumalai <kiran@scalex86.org>]

On Tue, Sep 27, 2005 at 03:36:40PM +0200, Bartlomiej Zolnierkiewicz wrote:
> On 9/7/05, Jens Axboe <axboe@suse.de> wrote:
> > On Wed, Sep 07 2005, Ravikiran G Thirumalai wrote:
> > > On Wed, Sep 07, 2005 at 11:19:24AM +0200, Jens Axboe wrote:
> > > > On Tue, Sep 06 2005, Ravikiran G Thirumalai wrote:
> > > > > The following patchset breaks down the global ide_lock to per-hwgroup lock.
> > > > > We have taken the following approach.
> > > >
> > > > Curious, what is the point of this?
> > > >
> > >
> >
> > I'm asking because I've never heard anyone complain about IDE lock
> > contention and a proper patch usually comes with analysis of why it is
> > needed.
> 
> Since ide_lock spinlock is used for all drives as queue lock and for all
> controllers as IDE lock I guess that with multiple controllers there is a lot
> contention on it...
> 
> Breaking ide_lock is fine with me however seeing numbers would
> greatly help in getting wider acceptance for this change, Ravikiran?
> 

With the lock breakdown, Iozone read performance went up by 5.5% on a 2 way
x86 xeon box, with two hwifs and two processes reading from disks connected
to each hwif.  There seems to be a small  regression on Iozone write
tests -- about 1.5%.  Maybe this is measurement noise as there is no apparent
reason for this.  We plan to run more tests to see if the regression for
writes is statistically significant.

Btw, there was some problem with the moving of tuning code in this patchset
causing disks not to work in DMA mode. We were fixing that; will publish a
newer patchset with test results soon.

Thanks,
Kiran