From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gentwo.org (gentwo.org [62.72.0.81]) (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 9305E1DFDB5; Thu, 17 Oct 2024 17:25:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.72.0.81 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729185960; cv=none; b=rwrznJq896if183++MEaWx5CjWkIYUSYKMDbUSX7HE2Nr2Y9LN0eFgyOydYASwl8uv58zY5ujC5Xj7lEe9IYg7BuXtOrDTXuIkFH614lcxbw1tjpN8EvKXz6SNUsHXeWUaIxilSS7xVaKWN6jDaRXD+oSaIwXAPpjPinOzA2MT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729185960; c=relaxed/simple; bh=oxTupLXSgxbLn39ngHQOrPR9z7y/bIXj7Kei68yHNAM=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=IZ7EGhZL6B0C655twwLjyqemPjJ/oZtWVwGI8pf+IdKAbY+O1c+J3s6qv955YiFP9tguJklg7fMqCs96/bmnqhK3pOI+ZIi7ogxexUbF73AzfrOyOPpq3hlBGvgtsfvQ4jpzKrr4WYJYWwtO0chaEb2E6X0fbsG/wOpoaxvoIVY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gentwo.org; spf=pass smtp.mailfrom=gentwo.org; dkim=pass (1024-bit key) header.d=gentwo.org header.i=@gentwo.org header.b=L0Gevzpo; arc=none smtp.client-ip=62.72.0.81 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gentwo.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gentwo.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=gentwo.org header.i=@gentwo.org header.b="L0Gevzpo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gentwo.org; s=default; t=1729184074; bh=oxTupLXSgxbLn39ngHQOrPR9z7y/bIXj7Kei68yHNAM=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=L0GevzpoDEAMzElBztpL1IWC/IxrvBuA849C4ewpzp9+I63Bjnl8V7oWWsDEi6x4u WXrb3V16oKlo/eebJBlEyHBU7XvC3VUmG7PzBVRAUR9VOlQ9nJrOZQg1XHxnszu91C Bv7KsLgC8BHeV1vx5Y1ITmA/7Wz6lNZzOUUmX/bk= Received: by gentwo.org (Postfix, from userid 1003) id C754540280; Thu, 17 Oct 2024 09:54:34 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id C5197400C9; Thu, 17 Oct 2024 09:54:34 -0700 (PDT) Date: Thu, 17 Oct 2024 09:54:34 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Ankur Arora cc: Catalin Marinas , linux-pm@vger.kernel.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, pbonzini@redhat.com, wanpengli@tencent.com, vkuznets@redhat.com, rafael@kernel.org, daniel.lezcano@linaro.org, peterz@infradead.org, arnd@arndb.de, lenb@kernel.org, mark.rutland@arm.com, harisokn@amazon.com, mtosatti@redhat.com, sudeep.holla@arm.com, misono.tomohiro@fujitsu.com, maobibo@loongson.cn, joao.m.martins@oracle.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH v8 01/11] cpuidle/poll_state: poll via smp_cond_load_relaxed() In-Reply-To: <87frowr0fo.fsf@oracle.com> Message-ID: References: <20240925232425.2763385-1-ankur.a.arora@oracle.com> <20240925232425.2763385-2-ankur.a.arora@oracle.com> <086081ed-e2a8-508d-863c-21f2ff7c5490@gentwo.org> <1e56e83e-83b3-d4fd-67a8-0bc89f3e3d20@gentwo.org> <87jze9rq15.fsf@oracle.com> <2c232dc6-6a13-e34b-bdcc-691c966796d4@gentwo.org> <87frowr0fo.fsf@oracle.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 On Wed, 16 Oct 2024, Ankur Arora wrote: > > The other core will wake our core up by sending an IPI. The IPI will > > invoke a scheduler function on our core and the WFE will continue. > > Why? The target core is not sleeping. It is *polling* on a memory > address (on arm64, via LDXR; WFE). Ergo an IPI is not needed to tell > it that a need-resched bit is set. The IPI is sent to interrupt the process that is not sleeping. This is done so the busy processor can reschedule the currently running process and respond to the event. It does not matter if the core is "sleeping" or not.