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Message-ID: <20230621073212.GC2046280@hirez.programming.kicks-ass.net>
Date: Wed, 21 Jun 2023 09:32:12 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Waiman Long <longman@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
x86@...nel.org, linux-pm@...r.kernel.org,
Robin Jarry <rjarry@...hat.com>, Joe Mario <jmario@...hat.com>
Subject: Re: [PATCH v2 5/5] x86/idle: Disable IBRS entering mwait idle and
enable it on wakeup
On Tue, Jun 20, 2023 at 10:06:25AM -0400, Waiman Long wrote:
> When a user sets "intel_idle.max_cstate=0", it will disable
> intel_idle and fall back to acpi_idle instead. The acpi_idle code
> will then call mwait_idle_with_hints() to enter idle state. So when
> X86_FEATURE_KERNEL_IBRS is enabled, it is necessary to disable IBRS
> within mwait_idle_with_hints() when IRQ was disabled to avoid performance
> degradation on silbing thread running user workload.
Urgh, no, just no. This is nasty.
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