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58cf9277-x86-time-dont-use-vTSC-if-host-guest-f...
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File 58cf9277-x86-time-dont-use-vTSC-if-host-guest-freqs-match.patch of Package xen.6641
References: bsc#1026236 # Commit 4fc380ac0077ecd6b0e0013ca7ca977cb7361662 # Date 2017-03-20 09:27:35 +0100 # Author Boris Ostrovsky <boris.ostrovsky@oracle.com> # Committer Jan Beulich <jbeulich@suse.com> x86/time: don't use virtual TSC if host and guest frequencies are equal Commit 82713ec8d2 ("x86: use native RDTSC(P) execution when guest and host frequencies are the same") left out optimization for PV guests when host and guest run at the same frequency. For such a case we should be able not to use virtual TSC regardless of whether we are runing before or after a migration (i.e. regardless of incarnation value). Suggested-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> [jb: retain parts of the original comment] Reviewed-by: Jan Beulich <jbeulich@suse.com> --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -1924,17 +1924,18 @@ void tsc_set_info(struct domain *d, d->arch.vtsc_offset = get_s_time() - elapsed_nsec; d->arch.tsc_khz = gtsc_khz ?: cpu_khz; set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000); + /* - * In default mode use native TSC if the host has safe TSC and: - * HVM/PVH: host and guest frequencies are the same (either - * "naturally" or via TSC scaling) - * PV: guest has not migrated yet (and thus arch.tsc_khz == cpu_khz) + * In default mode use native TSC if the host has safe TSC and + * host and guest frequencies are the same (either "naturally" or + * - for HVM/PVH - via TSC scaling). + * When a guest is created, gtsc_khz is passed in as zero, making + * d->arch.tsc_khz == cpu_khz. Thus no need to check incarnation. */ if ( tsc_mode == TSC_MODE_DEFAULT && host_tsc_is_safe() && - (has_hvm_container_domain(d) ? - (d->arch.tsc_khz == cpu_khz || - hvm_get_tsc_scaling_ratio(d->arch.tsc_khz)) : - incarnation == 0) ) + (d->arch.tsc_khz == cpu_khz || + (has_hvm_container_domain(d) && + hvm_get_tsc_scaling_ratio(d->arch.tsc_khz))) ) { case TSC_MODE_NEVER_EMULATE: d->arch.vtsc = 0;
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