Date: Thu, 14 Apr 2011 11:06:37 -0400 From: Jung-uk Kim <jkim@FreeBSD.org> To: Dimitry Andric <dim@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r220584 - in head/sys: amd64/amd64 i386/i386 Message-ID: <201104141106.40303.jkim@FreeBSD.org> In-Reply-To: <201104141044.55789.jkim@FreeBSD.org> References: <201104122349.p3CNn7kK039179@svn.freebsd.org> <4DA6D145.8070804@FreeBSD.org> <201104141044.55789.jkim@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
--Boundary-00=_A2wpNeamMJ/Vg7B Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline On Thursday 14 April 2011 10:44 am, Jung-uk Kim wrote: > On Thursday 14 April 2011 06:49 am, Dimitry Andric wrote: > > On 2011-04-14 00:27, Jung-uk Kim wrote: > > ... > > > > >> will still read 0 from MSR_MPERF, leading to a division by > > >> zero. Maybe just fallback to the second method in the 'else' > > >> branch then? > > > > > > That means your VM has broken CPUID support. To get there, it > > > has to meet two conditions, i.e., TSC is invariant and it has > > > APERF/MPERF MSRs. > > > > Well, VM hosts like VMware and VirtualBox usually just return the > > 'native' CPUID values to guests, but can't really support stuff > > like those MSRs, for all kinds of reasons. > > > > I was just looking at this from a viewpoint of "it worked for > > years, and now it broke". :) > > > > In any case, I don't see why a bit of defensive programming would > > be bad here, so I propose the following patch to revert to the > > 'old' way of estimating the rate, in case reading the MPERF MSR > > returns zero. > > I am going to test APERF & MPERF so that you don't need to do that > from there. Please stay tuned. Can you please test the attached patch? Thanks, Jung-uk Kim --Boundary-00=_A2wpNeamMJ/Vg7B Content-Type: text/plain; charset="iso-8859-1"; name="tsc.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="tsc.diff" Index: sys/x86/x86/tsc.c =================================================================== --- sys/x86/x86/tsc.c (revision 220613) +++ sys/x86/x86/tsc.c (working copy) @@ -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) { --Boundary-00=_A2wpNeamMJ/Vg7B--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201104141106.40303.jkim>