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 CEE0AEE4996 for ; Mon, 21 Aug 2023 12:46:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: List-Subscribe:List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: In-Reply-To:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: 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=HuqYrExYMQe3HvYp05QPHFyvgXkXFpoyeJ9CW+gjCok=; b=wSBqnYOOhqioAyiBK2+0v2pneH J0lW+sCG1hckiK2uWRKE9RmWjkgpYA+v8pKGOUNa+AjrpXQE3+P7ZAea+cbdauUeh5mjqkEtGkcE/ KWYi95A5Wy+hrwtqOXSq5bUUWw6p0NeJ+I/5IuFwsYltBqk27+PD2/DIV0SGLObJU5xxmpE6m4v48 SxeVGmqyYdHpFRNlAqGsgsdiH/RtNXmE9NNYjdqxIgbPQYuxuJyutS0UB5pxLw6002o9n8Cx88AT0 TO3jKC0msCIKdwx+rNmoP6bt/aFL0/2M6SzWxdlwQ+5sucCNNJmw1oVL3bmv4GL6uFcYhSzdWpRHc bE0ZoieA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qY4Ie-00E1ZC-2I; Mon, 21 Aug 2023 12:46:28 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qY4Ib-00E1YZ-12 for linux-arm-kernel@lists.infradead.org; Mon, 21 Aug 2023 12:46:26 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 37D0B615F2; Mon, 21 Aug 2023 12:46:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38BCCC433C9; Mon, 21 Aug 2023 12:46:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692621983; bh=QfHr3TwVh0T7XtdDdQup26sjK2MUEm2PDVaOMB9YabQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OItiQnv2kToKJYVpaO12QlNqdbLzISLy0lG6eDvWfj3XBoYT6B7es+0UmOQVby2wC U96R/UdUNJravQqH6qYfp44U59V9RP0Q2HTc0skh0p8DfMNSB3TQEoHnXlvhJuLKRv 3p4DVCDZIMe0M9m3dmR7DsuFgKbK710ftY/V/344ah0eLb+MmXpDOTuQN2OaL7ApMg W96iFF7QSqdaHvuGqpYQcJlohjvaGdhzO9wfjMQRXj4qehOZbMgCKgPuBqdCX+H37D JmA7jd6cKd+U48S9lQb0sJRpl0/lyJbt/GCQWusa/zhXpheL1qo82Jb0LHQrS5owP/ 3C/1+3iNS/4nQ== Date: Mon, 21 Aug 2023 13:46:18 +0100 From: Mark Brown To: Will Deacon Cc: Catalin Marinas , Benjamin Herrenschmidt , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64/fpsimd: Suppress SVE access traps when loading FPSIMD state Message-ID: <12a8953b-2182-43a6-8b4e-6026aa83bf4d@sirena.org.uk> References: <20230807-arm64-sve-trap-mitigation-v1-1-d92eed1d2855@kernel.org> <20230821121049.GA19670@willie-the-truck> MIME-Version: 1.0 In-Reply-To: <20230821121049.GA19670@willie-the-truck> X-Cookie: Do not write below this line. X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230821_054625_418705_DCF57C1C X-CRM114-Status: GOOD ( 21.68 ) 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: , Content-Type: multipart/mixed; boundary="===============3722930548168891456==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============3722930548168891456== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="8/R8UoP1GQFsbqkL" Content-Disposition: inline --8/R8UoP1GQFsbqkL Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Aug 21, 2023 at 01:10:50PM +0100, Will Deacon wrote: > On Mon, Aug 07, 2023 at 11:20:38PM +0100, Mark Brown wrote: > > I did some instrumentation which counted the number of SVE access traps > > and the number of times we loaded FPSIMD only register state for each task. > > Testing with Debian Bookworm this showed that during boot the overwhelming > > majority of tasks triggered another SVE access trap more than 50% of the > > time after loading FPSIMD only state with a substantial number near 100%, > > though some programs had a very small number of SVE accesses most likely > > from startup. There were few tasks in the range 5-45%, most tasks either > Do you have any performance numbers to motivate this change? It would be > interesting, for example, to see how changing the timeout value affects > the results for some real workloads. I agree, unfortunately I don't yet have a hardware setup so I can't do those benchmarks myself at the minute - I just have the access trap counting I mentioned in the commit message. Last time I saw numbers the access traps were about 70% of a syscall in a microbenchmark and we're already suppressing them for non-blocking syscalls so I'd not expect anything *too* revolutionary. --8/R8UoP1GQFsbqkL Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmTjXJoACgkQJNaLcl1U h9BIxwf/W/qEBRrqU2Vyd4/z4dVG+W54+stFaOqp4GsblUMLtOTqLElb+dNpcKw9 4/enu/53458MGm4tr8iGy6LcJBitSROXtX89LZfeddnFsmttA+RRA0jZGmRLbT3G Ia63OhHoJYrRkT7RrZVBomJgyQV86omq9Mf7mCttNchFywb9Cm7RaXpMwJ9lYxVo cvG8tQq/WnKSvOgs8eR+PfrN2wi//8cmIPFarH6a8pFNh0zbkV6vcvY+zOen6Y3W aSI+I+Nlt92BkrxNrG3X36GgIv0WRJzXoUfBQcqM0XN5mZNUAUP+5VulZ6nzQM5o GsF4QoZQ2b9mUWbKT4Qqsx4S95n+Mw== =Ko14 -----END PGP SIGNATURE----- --8/R8UoP1GQFsbqkL-- --===============3722930548168891456== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============3722930548168891456==--