Messages in this thread | | | Date | Thu, 6 Oct 2005 17:32:23 +0400 | From | Andrey Savochkin <> | Subject | Re: SMP syncronization on AMD processors (broken?) |
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On Thu, Oct 06, 2005 at 03:19:07PM +0200, Arjan van de Ven wrote: > On Thu, 2005-10-06 at 17:05 +0400, Kirill Korotaev wrote: > > Hello Linus, Andrew and others, > > > > Please help with a not simple question about spin_lock/spin_unlock on > > SMP archs. The question is whether concurrent spin_lock()'s should > > acquire it in more or less "fair" fashinon or one of CPUs can starve any > > arbitrary time while others do reacquire it in a loop. > > spinlocks are designed to not be fair. or rather are allowed to not be. > If you want them to be fair on x86 you need at minimum to put a > cpu_relax() in your busy loop...
The question was raised exactly because cpu_relax() doesn't help on these AMD CPUs.
Some Pentiums do more than expected from them, and the programs works in a very fair manner even without cpu_relax(), so the question boils down to whether there are some new AMD rules how to write such loops, is it a defect of the CPU, or if we are missing something else.
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