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Subject: Re: [fuse-devel] [PATCH v5 7/7] add a flag for per-operation O_DSYNC semantics
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From: Anton Altaparmakov <aia21@cam.ac.uk>
In-Reply-To: <CAFboF2y2skt=H4crv54shfnXOmz23W-shYWtHWekK8ZUDkfP=A@mail.gmail.com>
Date: Fri, 7 Nov 2014 08:43:00 +0200
Cc: Jeff Moyer <jmoyer@redhat.com>, linux-arch@vger.kernel.org,
        linux-aio@kvack.org, linux-nfs@vger.kernel.org,
        Volker Lendecke <Volker.Lendecke@sernet.de>,
        "Theodore Ts'o" <tytso@mit.edu>, linux-mm@kvack.org,
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        linux-api@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>, Tejun Heo <tj@kernel.org>,
        Milosz Tanski <milosz@adfin.com>, linux-fsdevel@vger.kernel.org,
        Michael Kerrisk <mtk.manpages@gmail.com>, ceph-devel@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>, ocfs2-devel@oss.oracle.com,
        Mel Gorman <mgorman@suse.de>
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References: <cover.1415220890.git.milosz@adfin.com> <c188b04ede700ce5f986b19de12fa617d158540f.1415220890.git.milosz@adfin.com> <x49r3xf28qn.fsf@segfault.boston.devel.redhat.com> <BF30FAEC-D4D3-4079-9ECD-2743747279BD@cam.ac.uk> <CAFboF2y2skt=H4crv54shfnXOmz23W-shYWtHWekK8ZUDkfP=A@mail.gmail.com>
To: Anand Avati <avati@gluster.org>
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Hi,

> On 7 Nov 2014, at 07:52, Anand Avati <avati@gluster.org> wrote:
> On Thu, Nov 6, 2014 at 8:22 PM, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
> > On 7 Nov 2014, at 01:46, Jeff Moyer <jmoyer@redhat.com> wrote:
> > Minor nit, but I'd rather read something that looks like this:
> >
> >       if (type == READ && (flags & RWF_NONBLOCK))
> >               return -EAGAIN;
> >       else if (type == WRITE && (flags & RWF_DSYNC))
> >               return -EINVAL;
> 
> But your version is less logically efficient for the case where "type == READ" is true and "flags & RWF_NONBLOCK" is false because your version then has to do the "if (type == WRITE" check before discovering it does not need to take that branch either, whilst the original version does not have to do such a test at all.
> 
> Seriously?

Of course seriously.

> Just focus on the code readability/maintainability which makes the code most easily understood/obvious to a new pair of eyes, and leave such micro-optimizations to the compiler..

The original version is more readable (IMO) and this is not a micro-optimization.  It is people like you who are responsible for the fact that we need faster and faster computers to cope with the inefficient/poor code being written more and more...

And I really wouldn't hedge my bets on gcc optimizing something like that.  The amount of crap assembly produced from gcc that I have seen over the years suggests that it is quite likely it will make a hash of it instead...

Best regards,

	Anton

> Thanks

-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
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