linux-kernel - Re: [PATCH 11/11] DIO: optimize cache misses in the submission path

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Date:	Mon, 8 Aug 2011 21:32:31 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 11/11] DIO: optimize cache misses in the submission path

> I bet we could default to using the smaller block size all the time, and
> still be able to detect when we don't have to do the sub-block zeroing.
> Maybe that would be a good follow-on patch.

It doesn't really matter because it's out of the fast path now.

> > +	/* 
> > +	 * Avoid references to bdev if not absolutely needed to give
> > +	 * the early prefetch in the caller enough time.
> > +	 */
> >  
> > -	if (offset & blocksize_mask) {
> > +	if (unlikely(offset & blocksize_mask)) {
> 
> You can't make this assumption.  Userspace controls what size/alignment
> of blocks to send in.

What assumption do you mean?

The code semantics are identical, just the place where I fetch
the block size is different (unless I missed something of course)


-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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