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Message-ID: <9eb8f395-c77f-a0bf-96b7-f1a3bb178c48@intel.com>
Date: Tue, 8 Nov 2022 10:27:56 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Pavel Machek <pavel@....cz>,
Andrew Cooper <Andrew.Cooper3@...rix.com>, degoede@...hat.com
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
antonio.gomez.iglesias@...ux.intel.com
Subject: Re: [PATCH 1/3] x86/tsx: Add feature bit for TSX control MSR support
On 9/12/22 16:39, Pawan Gupta wrote:
> Support for TSX control MSR is enumerated in MSR_IA32_ARCH_CAPABILITIES.
> This is different from how other CPU features are enumerated i.e. via
> CPUID. Enumerating support for TSX control currently has an overhead of
> reading the MSR every time which can be avoided.
I only see tsx_ctrl_is_supported() getting called in three places:
> 1 tsx.c tsx_clear_cpuid 138 } else if (tsx_ctrl_is_supported()) {
> 2 tsx.c tsx_dev_mode_disable 161 if (!boot_cpu_has_bug(X86_BUG_TAA) || !tsx_ctrl_is_supported() ||
> 3 tsx.c tsx_init 194 if (!tsx_ctrl_is_supported()) {
Those all look like boot-time things to me. Why does the overhead matter?
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