Messages in this thread | | | Date | Mon, 9 Jul 2007 12:55:01 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: queued spinlock code and results |
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On Mon, 9 Jul 2007, Davide Libenzi wrote: > > The always-lfence instruction in vadd-lock really is painfull though. > If numbers are close, and given that spinlock size considering structure > alignments should not matter much, wouldn't it be better to use a double > short and remove the 256 CPUs cap?
On x86? No.
There are no issues with the 255-CPU cap on 32-bit x86. It's just not relevant to anybody. So the _only_ thing that matters is speed and to a secondary degree size.
On x86-64, things are slightly different, and we would want to have at least the _capability_ to do 16 bits. So there might be a (somewhat weak) argument in favor of trying to share code.
But even then, size and performance are really the only things that matter, and if the 8/16-bit version is no slower, then I'd pick that by default, and suggest the 16/32-bit one to be enabled by CONFIG_MAX_CPU's being >=256 (at which point you can share the code with x86 anyway, since that just becomes the <256 cpu case).
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