From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 442953EBF01 for ; Fri, 29 May 2026 14:44:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780065894; cv=none; b=VYS694SJ3nNKWicsL7e6TOMndy3oHKhQZgDCQWkRIPFkFi7EOX9lOEORMTZO//qpg1dPRh8amNl4b1Gi+L2N820/EjusxZ0gZB3C2g/sdW3FvlkbcsjL2mnWPYFQAwnmD/HonhqRJcbKVKrJIffvNAykkp2Z3gGhTBSqbyGe2rU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780065894; c=relaxed/simple; bh=XDZ/SxBGCrg/x8VTpeNWDH8FGBeUvAAaHIVl6yABrEg=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=JLwOSois87qwLPyNDV7IPWv+MAhh1lQm+osz8jswwT0TfdU38EDZzuesuHvLZLnX62301NwoWDhWVvRbpZay4B6PQ8Pi8zRi8l8969sq2aheBC2oAP+LQgjVG0Icn4IPlGuGNhhYAioZH3hZDJoOR/I8/A/Cu/y9nbFYUAJ581E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Xlpo987Y; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Xlpo987Y" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-36603ad6709so11792584a91.2 for ; Fri, 29 May 2026 07:44:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1780065892; x=1780670692; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=L0mUatEZLxv6BfkDJUt0JsLCmFdWpOkVYX50Nml1d/w=; b=Xlpo987Y9FW1Kn+yUZcxdQJ7T+VIvE9Y0egMFMSeJY4DnBRf79F4/Tk4jeyuJboNdt d7cQI/3V7yCE9ZVOj3bB/O8CbV0a9L6DC/1GRJa9eeUfeLdnirTANmRuXRc7V+vlc10T CpLONgAlT+j0M6YQ2hk0PlJ95gCAeYu04RiAVLx4NeGYMPn96sIRjSXzhIsTfbBzuHHP XIqq7itNnKsV+SSvtKYBl2B3VxUDx/PEMvEF2q8Lx/jy+zRiqhoIiHWrTyQXjyvNKvzu HoWKtmDQGtVlecF8qFPqxttHYXf0y/Ex9ZITs/vKO9s0vcXLS+19vEilcC87XReNdTsv fGpw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780065892; x=1780670692; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=L0mUatEZLxv6BfkDJUt0JsLCmFdWpOkVYX50Nml1d/w=; b=MtE0l464WkMge5KTm1TpdixUfvtG5MvTC9uh/t6aWHdZhDnqjaKXy6ko88QhwOITnl XWAfadL0vV3DjhieQOMPAL1erQQx2s0EMoEXepGQT/smYhSfCSkemCAVgfoz/wLjQRWZ vTZ4TKOI4++3bffGJxu3zxpfnggg6E+tVJQYpRvn9ba2l4XwdUYdQQca7APBDUIw32Nu tX4eYaHxqKBJV9YO/UrzIvJvcUjuM79VK69hsuMlniD/yH/fxuK9KWOa53W+KDcMFuq/ 2KPCqGjGbbsxGzc5YfErW8i9iozTsH4XiJmaOsbGrK8OMIqPGslJFC9chUCKrj2IYVN6 NjkQ== X-Forwarded-Encrypted: i=1; AFNElJ/WfpqP2NnmhF9WrLeZr46YgKz+RdRJhjoEJDZu728D1/t9S9SUIrhpwNlm1YHhgCUZGG2bSSz5Ybs3@lists.linux.dev X-Gm-Message-State: AOJu0YwlyaIHAd5uGaofZjPTLxL1Rbv/4yGkD/t1ZQyXjf1PmUuY0Fa8 VRg8LU2ysV4hx4tmQuK70Wp7swe/8xOLk18F5DOU7t2187bfD0qSgKB3Tv0w5ePQ4YmdyxhXSHw DdWJ43A== X-Received: from pjbev8.prod.google.com ([2002:a17:90a:eac8:b0:36b:d883:98c2]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:e707:b0:36a:d6dd:9fee with SMTP id 98e67ed59e1d1-36bbcd6f8c3mr3583126a91.12.1780065892195; Fri, 29 May 2026 07:44:52 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 29 May 2026 07:43:48 -0700 In-Reply-To: <20260529144435.704127-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260529144435.704127-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.823.g6e5bcc1fc9-goog Message-ID: <20260529144435.704127-2-seanjc@google.com> Subject: [PATCH v4 01/47] x86/tsc: Never re-calibrate TSC frequency if its exact timing is known From: Sean Christopherson To: Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Sean Christopherson , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , John Stultz Cc: "H. Peter Anvin" , Rick Edgecombe , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, David Woodhouse , Tom Lendacky , Nikunj A Dadhania , David Woodhouse , Michael Kelley , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" 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 --- 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