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On Tue, 2005-11-29 at 23:38 -0800, Stephane Eranian wrote: > Nicholas, > > On Tue, Nov 29, 2005 at 03:29:26PM -0800, Nicholas Miell wrote: > > On Wed, 2005-11-30 at 00:17 +0100, Andi Kleen wrote: > > > On Tue, Nov 29, 2005 at 03:02:18PM -0800, Nicholas Miell wrote: > > > > On Tue, 2005-11-29 at 23:43 +0100, Andi Kleen wrote: > > > > > To give an bad analogy RDTSC usage in the last years is > > > > > like explicit spinning wait loops for delays in the earlier > > > > > times. They tended to work on some subset of computers, > > > > > but were always bad and caused problems and people eventually learned > > > > > it was better to use operating system services for this. > > > > > > > > And you are now suggesting people should use RDPMC instead of OS > > > > services? > > > > > > For any kind of timers they should use the OS service > > > (gettimeofday/clock_gettime). The OS will go to extraordinary > > > means to make it as fast as possible, but when it's slow > > > then because it's not possible to do it faster accurately > > > (that's the case right now modulo one possible optimization) > > > > > > For cycle counting where they previously used RDTSC they should > > > use RDPMC 0 now. > > > > Well, if that's all you want them to use RDPMC 0 for, why not just make > > PMCs programmable from userspace? > > > Simply because write a PERFSEL (i.e. an MSR) register is a privileged operation. Well, yeah. Design an API (or just steal from Solaris) and expose that to userspace. -- Nicholas Miell <nmiell@comcast.net> - 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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