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[2001:8b0:10b:1231::1]) by mx.google.com with ESMTPS id g1si2154463wmg.78.2019.01.29.07.17.10 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 29 Jan 2019 07:17:10 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) client-ip=2001:8b0:10b:1231::1; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b="ZM1/k2tv"; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Gjx0D2Hp2M6LW1jg+jUAo3bizRCgLIialUofJPerBW0=; b=ZM1/k2tvtEsbf4Yr3BAZU68P2 aGBBvKiUnJ+pC5oDVacZS5s3oyMtjDVlQLFFy8uUEUxLSZViutxEhxlBgCApf2IBQmpOcml9jf5Di f7H74YUBsdSIu4OA/tIhqmsDJUIB49ePezMZuopRrv4+la2rnZZ4x5SpBxtlBwOPUc93t1f2d0wEt QYsAZYHfu9GTwbS1+QIgz6TJr4hzdUdy6G4hycQWTDwJyqzrDUgwT/ZfkXqQpwcQnuY2idiRbxenN ADWS3xs25+rgsjAP8/QvH7fjMcKaT0IlurWuD8d2nBh5HNkIKCd/w5H7Zkw3Bkvpn7q5dNGx7JeOs +LXkOyuWA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1goV88-0002kd-8I; Tue, 29 Jan 2019 15:16:52 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AD64520101B8C; Tue, 29 Jan 2019 16:16:49 +0100 (CET) Date: Tue, 29 Jan 2019 16:16:49 +0100 From: Peter Zijlstra To: Suren Baghdasaryan Cc: gregkh@linuxfoundation.org, tj@kernel.org, lizefan@huawei.com, hannes@cmpxchg.org, axboe@kernel.dk, dennis@kernel.org, dennisszhou@gmail.com, mingo@redhat.com, akpm@linux-foundation.org, corbet@lwn.net, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 5/5] psi: introduce psi monitor Message-ID: <20190129151649.GA2997@hirez.programming.kicks-ass.net> References: <20190124211518.244221-1-surenb@google.com> <20190124211518.244221-6-surenb@google.com> <20190129123843.GK28467@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190129123843.GK28467@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000115, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 29, 2019 at 01:38:43PM +0100, Peter Zijlstra wrote: > On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote: > > + atomic_set(&group->polling, polling); > > + /* > > + * Memory barrier is needed to order group->polling > > + * write before times[] read in collect_percpu_times() > > + */ > > + smp_mb__after_atomic(); > > That's broken, smp_mb__{before,after}_atomic() can only be used on > atomic RmW operations, something atomic_set() is _not_. Also; the comment should explain _why_ not only what.