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From: Rusty Russell <rusty@rustcorp.com.au>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Chinner <david@fromorbit.com>, Jens Axboe <axboe@kernel.dk>,
        Minchan Kim <minchan@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Hugh Dickins <hughd@google.com>, "Michael S. Tsirkin" <mst@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 4/4] virtio_ring: unify direct/indirect code paths.
In-Reply-To: <20140529075256.GZ30445@twins.programming.kicks-ass.net>
References: <87oayh6s3s.fsf@rustcorp.com.au> <1401348405-18614-1-git-send-email-rusty@rustcorp.com.au> <1401348405-18614-5-git-send-email-rusty@rustcorp.com.au> <20140529075256.GZ30445@twins.programming.kicks-ass.net>
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Date: Thu, 29 May 2014 20:35:58 +0930
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Peter Zijlstra <peterz@infradead.org> writes:
> On Thu, May 29, 2014 at 04:56:45PM +0930, Rusty Russell wrote:
>> Before:
>> 	gcc 4.8.2: virtio_blk: stack used = 392
>> 	gcc 4.6.4: virtio_blk: stack used = 480
>> 
>> After:
>> 	gcc 4.8.2: virtio_blk: stack used = 408
>> 	gcc 4.6.4: virtio_blk: stack used = 432
>
> Is it worth it to make the good compiler worse? People are going to use
> the newer GCC more as time goes on anyhow.

No, but it's only 16 bytes of stack loss for a simplicity win:

 virtio_ring.c |  120 +++++++++++++++++++++-------------------------------------
 1 file changed, 45 insertions(+), 75 deletions(-)

Cheers,
Rusty.