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 X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F311C3A5A8 for ; Tue, 3 Sep 2019 07:13:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB2E6206B8 for ; Tue, 3 Sep 2019 07:13:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="eOf6lWVq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726473AbfICHNo (ORCPT ); Tue, 3 Sep 2019 03:13:44 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:42336 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726053AbfICHNo (ORCPT ); Tue, 3 Sep 2019 03:13:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=LfXrvAJ7nQoeTC4iaVaz4jsSr8XCOc8hcyp+iKwf00M=; b=eOf6lWVqK21zIHGXt/TWiBnTs +fN6KCAkxPGpd9nxtFWJ/3assrkapeFAG3RV6G3fABwRmkOq3H6vxIqGOIUQITnkGuFrZjIc1bTmk 3ehnqfXXcmhzDv7Yw8kBQtAbEyg0MpGXuMFCWIQ2ykiCy7AlIKoDQ8N41s9WVF7P/HQioY+E/agjp 4L3cJUF2FN2YUXDXfI9JrrapycrScQxn+ub0uduaH5wedj2Aqk/ZaDtqRbgx5YmtdvoBNtqwHxO07 pmlE3Q+9vWr5fDwa9Mp+I2tr//6Za09Mi4KK4quscbv04fHs+GJ56v0HrHEHmG5e0NlUFYxi/W5tH KICr3qrOg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i530L-0000jr-Cj; Tue, 03 Sep 2019 07:13:30 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4EDE8306010; Tue, 3 Sep 2019 09:12:50 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 594B529B9FF5D; Tue, 3 Sep 2019 09:13:26 +0200 (CEST) Date: Tue, 3 Sep 2019 09:13:26 +0200 From: Peter Zijlstra To: Christoph Hellwig Cc: Alexey Dobriyan , mingo@redhat.com, aarcange@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, dm-devel@redhat.com, axboe@kernel.dk Subject: Re: [dm-devel] [PATCH] sched: make struct task_struct::state 32-bit Message-ID: <20190903071326.GV2369@hirez.programming.kicks-ass.net> References: <20190902210558.GA23013@avx2> <20190903065155.GA28322@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190903065155.GA28322@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Sep 02, 2019 at 11:51:55PM -0700, Christoph Hellwig wrote: > On Tue, Sep 03, 2019 at 12:05:58AM +0300, Alexey Dobriyan wrote: > > 32-bit accesses are shorter than 64-bit accesses on x86_64. > > Nothing uses 64-bitness of ->state. > > > > Space savings are ~2KB on F30 kernel config. > > I guess we'd save even more when moving from a volatile to > WRITE_ONCE/READ_ONCE.. I doubt it; pretty much all accesses really should be using that. Not saying we shouldn't maybe do that; but that's going to be massive churn.