From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3505123CB; Wed, 28 May 2025 13:18:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748438289; cv=none; b=iv8vbPE+6URVp+mL0sdWjZ0b3wBNhquIzsd55JgTLG5z22fEQpyxKEK/RKMnzbNFXOX27KfRfKlXrUYv71iFNo+JlqKDEIZC2l01pIyuVsb93jo5O7mNQqwdIB6BIAbZOXSkKwcSWyBscfXRHSHlSQ3yIhDYdLserpaTlACrbSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748438289; c=relaxed/simple; bh=JyQ/g7Kg5zGeYkYRJRGiz+qenkQhnkpuUKlYzzPl8U4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=k10uxEPoW4O1DGTReVXmhqk2H7NJQUiLrzTLY/PqtDoCKVogPLnDC5hdp1IM4NePk0HAwPSA6zEjIgSUSxkG4Tu3SJFaX+xKf1GrUzN8l4eImPEG0NGTi+F/d1NVvJq6xLRg9jaYTNs7CCku47Kd1xhIaXPD3J7cBGgPDnVZYiU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=EyQhrn7j; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="EyQhrn7j" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=AVELsSfT+NEsd6GMqBswfz7jVJ/MdJvCvrkyarXhQCQ=; b=EyQhrn7jpycft0MeKIZGHyWnJS ibq1GqgdSdrU8tsQyawklHn+12vyeXjBzV6dery6l2SD8cOTNx5/oB1HNcGEL27lWhewnxWPye9Js nA79OsaIKp86WbLInP4ThC6poftelv6zYQUUzgfcoTLjXC6WNJkI5k9klFu3NHap01jEkk9HkQwIF 1727Xlwu+i8z1/1hu9w0iIHPk1ptBXXpHj7GNzKXQip+nCN7GB54WuQaRC65UPCcEp8Yt9Cv/ibPp 4gfdH+rM+/abnV9+WYPqErR8508sW8sjHs6pNJ4MCMF1J3d1B+PElS4/YArtLUsBm97tBYSup/C9n BerYQpKw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uKGfS-0000000DfhL-3vdd; Wed, 28 May 2025 13:18:03 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id D91C9300155; Wed, 28 May 2025 15:17:59 +0200 (CEST) Date: Wed, 28 May 2025 15:17:59 +0200 From: Peter Zijlstra To: "Rafael J. Wysocki" Cc: x86 Maintainers , LKML , Linux PM , Len Brown , Thomas Gleixner , Borislav Petkov , Dave Hansen , Artem Bityutskiy , "Gautham R. Shenoy" , Ingo Molnar , Todd Brandt Subject: Re: [PATCH v1 0/2] x86/smp: Fix power regression introduced by commit 96040f7273e2 Message-ID: <20250528131759.GA39944@noisy.programming.kicks-ass.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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2006806.PYKUYFuaPT@rjwysocki.net> On Wed, May 28, 2025 at 02:53:13PM +0200, Rafael J. Wysocki wrote: > Hi Everyone, > > Commit 96040f7273e2 ("x86/smp: Eliminate mwait_play_dead_cpuid_hint()") > that shipped in 6.15 introduced a nasty power regression on systems that > start with "nosmt" in the kernel command line which prevents it from entering > deep package idle states (for instance, PC10) later on. Idle power, including > power in suspend-to-idle, goes up significantly on those systems as a result. > > Address this by reverting commit 96040f7273e2 (patch [1/2]) and using a > different approach, which is to retain mwait_play_dead_cpuid_hint() and > still prefer it to hlt_play_dead() in case it is needed when cpuidle is > not available, but prefer cpuidle_play_dead() to it by default (patch [2/2]). I don't understand. The revert says the reason it regresses is that it goes into play_dead before cpuidle is initialized. The fix is then to call cpuidle first. But if cpuidle isn't initialized yet, how does that fix anything?