From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 BFEE7437472 for ; Tue, 28 Jul 2026 13:44:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785246290; cv=none; b=gmEsqSTqu1WQxizlO7KePjVCnfvR1pcZx6KMMj4k2u6O3jBv4LpeE+SF38BPu5EqqFBudehwQ2lo0Wu+do7AObzojPDTEV5KvE0S+Me90RFZUfyzHzS/AEquy1pxyiL6bNzpbjfe+9vNkPA9U1uGk7rvbfMDOx7MIz0UAYyi+IE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785246290; c=relaxed/simple; bh=APWWOBy6Z2o1X0eXiQIIHWjesUzKITlYIi8X6nxgBfM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ScMinlIgxecMz2d8Gg0dgaFh4/cRPBYEhK+F3zG42iyuxiiiMozaBQwr4om1USi6NMC+mndLnNbsqCYUSB6YwFQNES1OB/f3IN5w4MJS7K5OgAQ8Hk/iUFM1qbgsnv2aiX0RVaqcnwQPaYdUTdKLf2uxSdNCdvU1o8e77W99Bts= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Ub7WEAwd; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass 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="Ub7WEAwd" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=APWWOBy6Z2o1X0eXiQIIHWjesUzKITlYIi8X6nxgBfM=; b=Ub7WEAwdnufeznZJ7HfSZDqsWC OnTVzTC7S7ySgY2LhtXcaJ+3EpFdMOWXAh7CgOZ4JJ8vOg8M0dHWeTuEqvRtGETidAtm8vYZnJJku LthHg1ggANAY3iOSb91W+qFh+cgQBwhF3hauPJ99ImxqE5sl0clIY5FNhlSIuXmY+z/w8aWae/2NE BziNyn5DWB7vPf4+K0ZlS7tNzQxP9IMK3mDA1NkhU4AXqhnd6yRgRlaYDrPD+OxYxNHMTntA1dbT5 1GXuLLmm/oMafwbmHqNr5RzAUbJERLFoVTE5YRfH2hLICi7Nx6cetR7RkIM4J253XgC3d8J3fAo2d V0JEC2qw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1woi6m-00000004z9M-00Js; Tue, 28 Jul 2026 13:44:36 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 555B5300969; Tue, 28 Jul 2026 15:44:34 +0200 (CEST) Date: Tue, 28 Jul 2026 15:44:34 +0200 From: Peter Zijlstra To: Jing Wu Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , "Paul E. McKenney" , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Qiliang Yuan , Jian Zhang Subject: Re: [PATCH] x86/aperfmperf: Refresh stale sample via IPI for busy NOHZ_FULL CPUs Message-ID: <20260728134434.GU751831@noisy.programming.kicks-ass.net> References: <20260728-bug-isolatecpu-cpufreq-v1-1-e95d34db8bcd@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260728-bug-isolatecpu-cpufreq-v1-1-e95d34db8bcd@gmail.com> On Tue, Jul 28, 2026 at 07:27:54PM +0800, Jing Wu wrote: > An isolated CPU covered by nohz_full stops its periodic tick once it > has only one runnable task, since sched_can_stop_tick() only checks > scheduling-class fairness and has no notion of cpufreq reporting > needs. arch_scale_freq_tick() runs only from scheduler_tick(), so > cpu_samples for that CPU is never refreshed again. Sending IPIs to NOHZ_FULL Cpus should be a no-no.