[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 01/04/2016 07:59 PM, Haozhong Zhang wrote: 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. -borisIn 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. OK --- I was looking at tsc_set_info()'s TSC_MODE_NEVER_EMULATE path but now I realize that we don't use scaling in that mode (right?). Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Haozhongxen/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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