[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20110819155534.GA13464@redhat.com>
Date: Fri, 19 Aug 2011 11:55:34 -0400
From: Vivek Goyal <vgoyal@...hat.com>
To: Andi Kleen <andi@...stfloor.org>
Cc: Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, hch@...radead.org,
Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [PATCH 10/11] VFS: Cache request_queue in struct block_device
On Fri, Aug 19, 2011 at 05:36:22PM +0200, Andi Kleen wrote:
> On Fri, Aug 19, 2011 at 10:14:09AM -0400, Vivek Goyal wrote:
> > On Thu, Aug 18, 2011 at 02:03:56PM -0700, Andi Kleen wrote:
> > >
> > > >Is the performance gain because of this one less dereference really
> > > >substantial.
> > > Yes it is measurable on a large macro benchmark.
> > >
> > > The gain is from doing the prefetch early enough, and that needs the
> > > additional pointer.
> >
> > So it gives you extra .3% (as mentioned in your first mail). IMHO, for
> > .3% we should not cache extra request queue pointer.
>
> Note this is on a benchmark which is primarily userland. Kernel
> is only a small part, so it's a much higher percentage for the kernel
> time.
>
> Also on that large benchmark it's hard to any improvement at all,
> and this isn't even a particularly ugly or intrusive change.
> Not sure why you're against it.
Primarily because of code complexity. We are stashing away a pointer and
not taking any reference anywhere. So I am not even sure who is making
sure that request queue is not gone and there are no comments in the code
about why we are stashing a pointer and how are we making sure that
request queue is around for the lifetime of bdev.
Thanks
Vivek
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists