linux-kernel - Re: [PATCH 4/4] virtio_ring: unify direct/indirect code paths.

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Message-ID: <87iooo7skp.fsf@rustcorp.com.au>
Date:	Thu, 29 May 2014 20:35:58 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Jens Axboe <axboe@...nel.dk>, Minchan Kim <minchan@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 4/4] virtio_ring: unify direct/indirect code paths.

Peter Zijlstra <peterz@...radead.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.
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