Messages in this thread | | | Date | Thu, 2 Nov 2006 11:24:27 +0100 | From | Jörn Engel <> | Subject | historical micro-optimizations (Re: [PATCH 1/1] fat: improve sync performance by grouping writes revised again) |
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On Wed, 1 November 2006 15:52:09 -0500, Phillip Susi wrote: > > In other words, the only time this micro optimization will be of benefit > is if you are erroring out most of the time rather than only under > exceptional conditions, AND the error label isn't too far away for a > conditional branch to reach. In other words, just don't do it ;)
The difference was in code size, so the icache impact would have benefitted the good case as well. "was" and "would have" because I finally got off my lazy arse and tested the code. With gcc 4.12 both variants compiled to exactly the same code. With 2.95 there was a one instruction (2 bytes) difference.
I didn't test all the versions in between, but the advantage is definitely a thing of the past.
And even if the 2 byte difference still existed, it wouldn't really matter much, we all agree on that. That's why I said:
> >Both methods definitely work. Whether one is preferrable over the > >other is imo 90% taste and maybe 10% better code on some architecture. > >So just pick what you prefer.
The only thing I was arguing was that one method would not work - it does. So I hope this was sufficient distraction for everyone and we can get back to work. :)
Jörn
-- You can't tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don't try to second guess and put in a speed hack until you've proven that's where the bottleneck is. -- Rob Pike - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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