[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PATCH v4 01/47] x86/tsc: Never re-calibrate TSC frequency if its exact timing is known
- To: Paolo Bonzini <pbonzini@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, Kiryl Shutsemau <kas@xxxxxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Wei Liu <wei.liu@xxxxxxxxxx>, Dexuan Cui <decui@xxxxxxxxxxxxx>, Long Li <longli@xxxxxxxxxxxxx>, Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>, Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>, Jan Kiszka <jan.kiszka@xxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, John Stultz <jstultz@xxxxxxxxxx>
- From: Sean Christopherson <seanjc@xxxxxxxxxx>
- Date: Fri, 29 May 2026 07:43:48 -0700
- Authentication-results: eu.smtp.expurgate.cloud; dkim=pass header.s=20251104 header.d=google.com header.i="@google.com" header.h="Cc:To:From:Subject:Message-ID:References:Mime-Version:In-Reply-To:Date:Reply-To"
- Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>, Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stephen Boyd <sboyd@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-coco@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, David Woodhouse <dwmw@xxxxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Nikunj A Dadhania <nikunj@xxxxxxx>, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, Michael Kelley <mhklinux@xxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Delivery-date: Fri, 29 May 2026 14:45:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Don't re-calibrate the TSC frequency if the TSC is known to run at a fixed
frequency. In practice, this is likely one big nop, as re-calibration is
used only for SMP=n kernels, and only for hardware that is 20+ years old,
i.e. is extremely unlikely to collide with TSC_KNOWN_FREQ.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kernel/tsc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index c5110eb554bc..08cf6625d484 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -946,7 +946,8 @@ void recalibrate_cpu_khz(void)
return;
cpu_khz = x86_platform.calibrate_cpu();
- tsc_khz = x86_platform.calibrate_tsc();
+ if (!boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ))
+ tsc_khz = x86_platform.calibrate_tsc();
if (tsc_khz == 0)
tsc_khz = cpu_khz;
else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
--
2.54.0.823.g6e5bcc1fc9-goog
|
