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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0F3B9C433E1 for ; Mon, 20 Jul 2020 10:46:18 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CC59420773 for ; Mon, 20 Jul 2020 10:46:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="KJwiVV40" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC59420773 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=EGkA15Ox1FHZCWGJD1h9ArTFfZ+SP9KRBfxguq6wr1k=; b=KJwiVV40Yss8i5kkagNr7yW7g 2mDoj8zOof6KptK+P603BDvMK4sjwKy+4nDB95S91friCX3HmFAtwrnNuGkPrz95EcXQ80LaSV1S2 u0vwM4D1SGsFY/gYdGe+3vpIU/jJRe6W8UBPcIKSyCgFMfY7I38vINGgEH3zT/IzLk6ccW2YShNTX Gzq2oSUk5JJy3BwRzHatAmaEwbz/cUo7m+7zDnHl2Sm1OUNs9ENtgvygYq2JOOCVgV9zVHLof3ICt cMQD3f3uTPTPeaQb35JCMz+mPrPRD0hADfP2ijeHnzcY5HSF0YwmPncSIk5SHg3TQ/tJ53JzIghIS 4ivquM76w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxTHt-0003Cd-To; Mon, 20 Jul 2020 10:44:49 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxTHr-0003C4-6C for linux-arm-kernel@lists.infradead.org; Mon, 20 Jul 2020 10:44:48 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D629FD6E; Mon, 20 Jul 2020 03:44:43 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D357B3F66E; Mon, 20 Jul 2020 03:44:42 -0700 (PDT) Date: Mon, 20 Jul 2020 11:44:40 +0100 From: Dave Martin To: Mark Brown Subject: Re: [PATCH v3 0/8] arm64/sve: First steps towards optimizing syscalls Message-ID: <20200720104438.GH30452@arm.com> References: <20200629133556.39825-1-broonie@kernel.org> <20200715164931.GC30452@arm.com> <20200715171116.GK5431@sirena.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200715171116.GK5431@sirena.org.uk> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200720_064447_281392_3BB4261C X-CRM114-Status: GOOD ( 16.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Julien Grall , Catalin Marinas , zhang.lei@jp.fujitsu.com, Will Deacon , linux-arm-kernel@lists.infradead.org, Daniel Kiss Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 15, 2020 at 06:11:16PM +0100, Mark Brown wrote: > On Wed, Jul 15, 2020 at 05:49:34PM +0100, Dave Martin wrote: > > > I wonder whether we ought to accompany this with a crude mechanism to > > choose dynamically between setting TIF_SVE_NEEDS_FLUSH and keeping the > > old behaviour. > > > My concern with doing this unconditionally has been that we can end up > > with TIF_SVE permanently stuck on, which increases the per-task overhead. > > This is not a worry if the user task really does use SVE once per > > context switch, but not so good if, say, the libc startup probes for > > SVE to initialise some internal logic but the task otherwise doesn't > > use it. (This is just a worry: I haven't looked for evidence to support > > it.) > > Yes, it's a concern. My thought was to follow this up with something > which copies what some of the other architectures are doing for FP > registers and go back to the existing behaviour after a certain number > of syscalls. That has a bunch of room for debate and bikeshedding about > what exactly an appropriate number might be of course. Ack, that sounds like a fair approach. Of course, we could try to implement some kind of clever backoff but it's probably not worth it for now. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel