From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8BFC6C36018 for ; Tue, 17 Sep 2024 11:54:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: Message-ID:Date:References:In-Reply-To:Subject:Cc:To:From:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=7bX+ckDiWzV0UXiUsEpBvHAAjmkCz9ocHzwV5JJ1Gn4=; b=f21xKJu7eXyPFyK0DcOGc2npuA nJSyvrqufrYmVA57M3hfOKCkzPvLJ6/hBVlYiCpXROXQgwxefCfcFap1q3k258jXpWNv0XNIzh/xp LAGAX0aacloQiw+tQtpVzfJ2BTIwPCT2wbEFMYR2iE8DIt8DCz+aW/23YPkTaLKrdxYoh/KqzOwBy CwzuaCKMGlvUMBRotlAl1rC+xuEqq75b1E2ycV4eIucptzj9rnRA/N8+/OoFdhq3of67HOeBw0qB+ SIxdT67ZtrwKpgioe1uugA8Tm5wJKfhOJuNXE7gdtPEtq/zSwOw3b7hrsBA1OXe0FbGYB/qccfWMM 3oiGxgPA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1sqWmP-000000065CF-0HsC; Tue, 17 Sep 2024 11:54:01 +0000 Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1sqWlG-0000000653c-2t15 for linux-arm-kernel@lists.infradead.org; Tue, 17 Sep 2024 11:52:53 +0000 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1726573969; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7bX+ckDiWzV0UXiUsEpBvHAAjmkCz9ocHzwV5JJ1Gn4=; b=Op8M+Ud/ecXwHOTy7YoUTH4slRc/9pzpxC5sgAbCKhScsfynbjtvzjn7cI2VkPtpaHNByX 6lDCZXjvLs1v5TxMEN0E5LIQFZmHVb8+FsmBvsCGeD9e55FZ0mtwfU0KHpqR/3mwHJNyj5 RxL8beQJgpw/sg3Cx9smitqJm9CAimomZxHQycly883Y7B0DFZiDDnX6887epqDFHeXqyP 6XY5FHyUejTAz1HsZYNaI/BcL6pnFZyIYyC4c1KuHBemn88f9eBxsFnYyuPydGqo9nhV9Q VbvIEW4dOOiGVjm7zccRVtSfsK5R8tJDEYbkkVE3k6CIHccCilknBxwF42Q3Fg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1726573969; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7bX+ckDiWzV0UXiUsEpBvHAAjmkCz9ocHzwV5JJ1Gn4=; b=Nv/BsxsS8N1MMLS0Mu4yS1B+iTF5E4Cmt408LhLBA/k+P/2xsFm9tPkhB/8+UpN3tp9U+F oG+6WW/C6AQoWtCw== To: Christoph Lameter via B4 Relay , Catalin Marinas , Will Deacon , Peter Zijlstra , Ingo Molnar , Waiman Long , Boqun Feng Cc: Linus Torvalds , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, "Christoph Lameter (Ampere)" Subject: Re: [PATCH v3] Avoid memory barrier in read_seqcount() through load acquire In-Reply-To: <20240912-seq_optimize-v3-1-8ee25e04dffa@gentwo.org> References: <20240912-seq_optimize-v3-1-8ee25e04dffa@gentwo.org> Date: Tue, 17 Sep 2024 13:52:48 +0200 Message-ID: <87o74m1oq7.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240917_045250_891597_19846CDF X-CRM114-Status: GOOD ( 10.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 12 2024 at 15:44, Christoph Lameter via wrote: $Subject: ..... You still fail to provide a proper subsystem prefix. It's not rocket science. https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#patch-subject > From: "Christoph Lameter (Ampere)" > > Some architectures support load acquire which can save us a memory > barrier and save some cycles. > > A typical sequence > > do { > seq = read_seqcount_begin(&s); > > } while (read_seqcount_retry(&s, seq); > > requires 13 cycles on ARM64 for an empty loop. Two read memory > barriers are needed. One for each of the seqcount_* functions. > > We can replace the first read barrier with a load acquire of > the seqcount which saves us one barrier. We .... Please write changelogs using passive voice. 'We' means nothing here. Thanks, tglx