On 02/26/10 12:24, Ingo Molnar wrote:
There is a way to query the CPU for 'architectural perfmon' though, via CPUID
alone - that is how we set the X86_FEATURE_ARCH_PERFMON shortcut. The logic
is:
if (c->cpuid_level> 9) {
unsigned eax = cpuid_eax(10);
/* Check for version and the number of counters */
if ((eax& 0xff)&& (((eax>>8)& 0xff)> 1))
set_cpu_cap(c, X86_FEATURE_ARCH_PERFMON);
}
But emulating that doesnt solve the problem: as OSs generally dont key their
PMU drivers off the relatively new 'architectural perfmon' CPUID detail, but
based on much higher level CPUID attributes. (like Intel/AMD)
Right, there is far more to it than just the arch-perfmon feature. They
still need to query cpuid 0x0a for counter size, number of counters and
stuff like that.
Cheers,
Jes
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