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x86: Fall back to leaf 0x16 if TSC frequency is obtained by CPUID and

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leaf 0x15 is not functional.

This should improve automatic TSC frequency determination on
Skylake/Kabylake/... families, where 0x15 exists but does not provide
all necessary information.  SDM contains relatively strong wording
against such uses of 0x16, but Intel does not give us any other way to
obtain the frequency. Linux did the same in the commit
604dc9170f2435d27da5039a3efd757dceadc684.

Based on submission by:	Neel Chauhan <neel@neelc.org>
PR:	240475
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D21777
This commit is contained in:
Konstantin Belousov 2019-09-25 13:36:56 +00:00
parent df1bc27a0c
commit a9d0e0071c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=352684
1 changed files with 18 additions and 4 deletions
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22
sys/x86/x86/tsc.c
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@ -134,7 +134,11 @@ tsc_freq_vmware(void)
/*
* Calculate TSC frequency using information from the CPUID leaf 0x15
* 'Time Stamp Counter and Nominal Core Crystal Clock'. It should be
* 'Time Stamp Counter and Nominal Core Crystal Clock'. If leaf 0x15
* is not functional, as it is on Skylake/Kabylake, try 0x16 'Processor
* Frequency Information'. Leaf 0x16 is described in the SDM as
* informational only, but if 0x15 did not work, and TSC calibration
* is disabled, it is the best we can get at all. It should still be
* an improvement over the parsing of the CPU model name in
* tsc_freq_intel(), when available.
*/
@ -146,10 +150,20 @@ tsc_freq_cpuid(void)
if (cpu_high < 0x15)
return (false);
do_cpuid(0x15, regs);
if (regs[0] == 0 || regs[1] == 0 || regs[2] == 0)
if (regs[0] != 0 && regs[1] != 0 && regs[2] != 0) {
tsc_freq = (uint64_t)regs[2] * regs[1] / regs[0];
return (true);
}
if (cpu_high < 0x16)
return (false);
tsc_freq = (uint64_t)regs[2] * regs[1] / regs[0];
return (true);
do_cpuid(0x16, regs);
if (regs[0] != 0) {
tsc_freq = (uint64_t)regs[0] * 1000000;
return (true);
}
return (false);
}
static void