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Re: [PATCH linux-next] x86/xen/time: prefer tsc as clocksource when it is invariant
- To: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Fri, 9 Dec 2022 14:32:15 -0500
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- Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Anthony Liguori <aliguori@xxxxxxxxxx>, David Reaver <me@xxxxxxxxxxxxxxx>, Brendan Gregg <brendan@xxxxxxxxx>
- Delivery-date: Fri, 09 Dec 2022 19:32:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12/8/22 11:36 AM, Krister Johansen wrote:
+ /*
+ * As Dom0 is never moved, no penalty on using TSC there.
+ *
+ * If the guest has invariant tsc, then set xen_clocksource rating
+ * below that of the tsc so that the system prefers tsc instead. This
+ * check excludes PV domains, because PV is unable to guarantee that the
+ * guest's cpuid call has been intercepted by the hypervisor.
+ */
+ if (xen_initial_domain()) {
xen_clocksource.rating = 275;
+ } else if ((xen_hvm_domain() || xen_pvh_domain()) &&
+ boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+ boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+ !check_tsc_unstable()) {
+ xen_clocksource.rating = 299;
+ }
What if RDTSC is intercepted?
-boris
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