Date: Thu, 14 Apr 2011 17:50:26 +0000 (UTC) From: Jung-uk Kim <jkim@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r220637 - head/sys/x86/x86 Message-ID: <201104141750.p3EHoQbC042617@svn.freebsd.org>
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Author: jkim Date: Thu Apr 14 17:50:26 2011 New Revision: 220637 URL: http://svn.freebsd.org/changeset/base/220637 Log: Work around an emulator problem where virtual CPU advertises TSC is P-state invariant and APERF/MPERF MSRs exist but these MSRs never tick. When we calculate effective frequency from cpu_est_clockrate(), it caused panic of division-by-zero. Now we test whether these MSRs actually increase to avoid such foot-shooting. Reported by: dim Tested by: dim Modified: head/sys/x86/x86/tsc.c Modified: head/sys/x86/x86/tsc.c ============================================================================== --- head/sys/x86/x86/tsc.c Thu Apr 14 17:42:21 2011 (r220636) +++ head/sys/x86/x86/tsc.c Thu Apr 14 17:50:26 2011 (r220637) @@ -183,8 +183,18 @@ probe_tsc_freq(void) if (cpu_high >= 6) { do_cpuid(6, regs); - if ((regs[2] & CPUID_PERF_STAT) != 0) - tsc_perf_stat = 1; + if ((regs[2] & CPUID_PERF_STAT) != 0) { + /* + * XXX Some emulators expose host CPUID without actual + * support for these MSRs. We must test whether they + * really work. + */ + wrmsr(MSR_MPERF, 0); + wrmsr(MSR_APERF, 0); + DELAY(10); + if (rdmsr(MSR_MPERF) > 0 && rdmsr(MSR_APERF) > 0) + tsc_perf_stat = 1; + } } if (tsc_skip_calibration) {
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