[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 04/13] x86/time.c: Scale host TSC in pvclock properly
On 01/04/16 13:09, Boris Ostrovsky wrote: > On 12/30/2015 10:03 PM, Haozhong Zhang wrote: > >This patch makes the pvclock return the scaled host TSC and > >corresponding scaling parameters to HVM domains if guest TSC is not > >emulated and TSC scaling is enabled. > > > >Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx> > >--- > >Changes in v3: > > (addressing Boris Ostrovsky's comments) > > * No changes in fact. tsc_set_info() does not set d->arch.vtsc to 0 > > if host_tsc_is_safe() is not satisfied, so it is safe to use > > d->arch.vtsc_to_ns here. > > I don't think I understand your argument here. I think last time we decided > that vtsc_to_ns can be used only if TSC is constant. > > -boris > In tsc_set_info(), if TSC scaling is available and host has X86_FEATURE_TSC_RELIABLE (checked by host_tsc_is_safe()), vtsc is left to 0. And looking at init_amd() and init_intel(), X86_FEATURE_CONSTANT_TSC is available whenever X86_FEATURE_TSC_RELIABLE is available as well. Therefore, when vtsc_to_ns is used in __update_vcpu_system_time(), we can always ensure that host has X86_FEATURE_CONSTANT_TSC and do not need to recheck it there. Haozhong > > > > xen/arch/x86/time.c | 16 ++++++++++++---- > > 1 file changed, 12 insertions(+), 4 deletions(-) > > > >diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c > >index d83f068..b31634a 100644 > >--- a/xen/arch/x86/time.c > >+++ b/xen/arch/x86/time.c > >@@ -815,10 +815,18 @@ static void __update_vcpu_system_time(struct vcpu *v, > >int force) > > } > > else > > { > >- tsc_stamp = t->local_tsc_stamp; > >- > >- _u.tsc_to_system_mul = t->tsc_scale.mul_frac; > >- _u.tsc_shift = (s8)t->tsc_scale.shift; > >+ if ( has_hvm_container_domain(d) && cpu_has_tsc_ratio ) > >+ { > >+ tsc_stamp = hvm_funcs.scale_tsc(v, > >t->local_tsc_stamp); > >+ _u.tsc_to_system_mul = d->arch.vtsc_to_ns.mul_frac; > >+ _u.tsc_shift = d->arch.vtsc_to_ns.shift; > >+ } > >+ else > >+ { > >+ tsc_stamp = t->local_tsc_stamp; > >+ _u.tsc_to_system_mul = t->tsc_scale.mul_frac; > >+ _u.tsc_shift = (s8)t->tsc_scale.shift; > >+ } > > } > > _u.tsc_timestamp = tsc_stamp; > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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