Messages in this thread | | | Date | Wed, 9 Jul 2014 11:19:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V4 1/2] perf ignore LBR and extra_regs. |
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On Tue, Jul 08, 2014 at 09:49:40AM -0700, kan.liang@intel.com wrote: > + /* > + * Access LBR MSR may cause #GP under certain circumstances. > + * E.g. KVM doesn't support LBR MSR > + * Check all LBT MSR here. > + * Disable LBR access if any LBR MSRs can not be accessed. > + */ > + if (x86_pmu.lbr_nr) { > + access = check_msr(x86_pmu.lbr_tos); > + for (i = 0; i < x86_pmu.lbr_nr; i++) { > + access &= check_msr(x86_pmu.lbr_from + i); > + access &= check_msr(x86_pmu.lbr_to + i); > + } > + if (!access) > + x86_pmu.lbr_nr = 0; > + }
You _could_ write that as:
if (x86_pmu.lbr_nr) { if (!check_msr(x86_pmu.lbr_tos)) x86_pmu.lbr_nr = 0; for (i = 0; i < x86_pmu.lbr_nr; i++) { if (!(check_msr(x86_pmu.lbr_from + i) && check_msr(x86_pmu.lbr_to + i))) x86_pmu.lbr_nr = 0; } }
There is no point in checking any more MSRs after the first fail after all. [unhandled content-type:application/pgp-signature] | |