From patchwork Wed May 28 12:54:49 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Rafael J. 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Wysocki" To: x86 Maintainers Cc: LKML , Linux PM , Len Brown , Peter Zijlstra , Thomas Gleixner , Borislav Petkov , Dave Hansen , Artem Bityutskiy , "Gautham R. Shenoy" , Ingo Molnar , Todd Brandt Subject: [PATCH v1 2/2] x86/smp: Prefer cpuidle_play_dead() to mwait_play_dead_cpuid_hint() Date: Wed, 28 May 2025 14:54:49 +0200 Message-ID: <3633769.iIbC2pHGDl@rjwysocki.net> In-Reply-To: <2006806.PYKUYFuaPT@rjwysocki.net> References: <2006806.PYKUYFuaPT@rjwysocki.net> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CLIENT-IP: 5.63.189.50 X-CLIENT-HOSTNAME: 5.63.189.50 X-VADE-SPAMSTATE: clean X-VADE-SPAMCAUSE: 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 X-DCC--Metrics: v370.home.net.pl 1024; Body=12 Fuz1=12 Fuz2=12 From: "Rafael J. Wysocki" Currently, mwait_play_dead_cpuid_hint() looks up the MWAIT hint of the deepest idle state by inspecting CPUID leaf 0x05 with the assumption that, if the number of sub-states for a given major C-state is nonzero, those sub-states are always represented by consecutive numbers starting from 0. This assumption is not based on the documented platform behavior and in fact it is not met on recent Intel platforms (eg. Sierra Forest). For this reason, it is better to let the cpuidle driver for the given platform put CPUs going offline into appropriate idle state and only if that fails, fall back to mwait_play_dead_cpuid_hint(), which may still be the next best "play dead" variant if cpuidle is not available. For example, when "nosmt" is passed to the kernel in the command line, SMT siblings are disabled early, before cpuidle gets ready, but they need to be put into sufficiently deep idle states to allow the whole processor to reach deep package idle states, like PC10, later on. Tested-by: Todd Brandt Signed-off-by: Rafael J. Wysocki --- arch/x86/kernel/smpboot.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1377,9 +1377,10 @@ play_dead_common(); tboot_shutdown(TB_SHUTDOWN_WFS); + /* Each call in the following sequence returns only on errors. */ + cpuidle_play_dead(); mwait_play_dead_cpuid_hint(); - if (cpuidle_play_dead()) - hlt_play_dead(); + hlt_play_dead(); } #else /* ... !CONFIG_HOTPLUG_CPU */