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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 436EAC4708E for ; Tue, 3 Jan 2023 10:07:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236997AbjACKHE (ORCPT ); Tue, 3 Jan 2023 05:07:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236812AbjACKGt (ORCPT ); Tue, 3 Jan 2023 05:06:49 -0500 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3096B12A for ; Tue, 3 Jan 2023 02:06:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To: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=4coSDhKU7mwRMnUBHyZf53rh/zHTShyJKZjrQJqxxZQ=; b=B12V0JeslL/XIkP4Z0lltsBBWc tZfAKB3JMY2U5lPpdVnMCkPvGczQgL1+b/2r2g+EqYedCqWcm8B0KryJnEicwXfHgzJY2masjoF5G Fkj2Sv1EeyWY8ckdQ5TCl7O8l3OP4iNffTqkUi6KUhBMCvW0FbKMQSnEDX27CEHgggGkBn/sFB4zc iBhIdqNwZ7QDp4Um4klM1db2XMzsCGv08GUDglexnqvEah9iKrNEu+TWfamME0iqX5IP9ARs9HRS+ n3CEWveF+U3eDsbkiovi2+ebb4u1rwhW1/okbMbLc9ywBwOLdm1Jyize/tnfpw16eebMsnaDUdpRS ZqBUObGQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:35908) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pCeBw-0005Bw-TV; Tue, 03 Jan 2023 10:06:44 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1pCeBu-0001xj-1a; Tue, 03 Jan 2023 10:06:42 +0000 Date: Tue, 3 Jan 2023 10:06:42 +0000 From: "Russell King (Oracle)" To: Hui Tang Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [bug-report] possible performance problem in ret_to_user_from_irq Message-ID: References: <7ecb8f3c-2aeb-a905-0d4a-aa768b9649b5@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7ecb8f3c-2aeb-a905-0d4a-aa768b9649b5@huawei.com> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 26, 2022 at 04:45:20PM +0800, Hui Tang wrote: > hi folks. > > I found a performance problem which is introduced by commit > 32d59773da38 ("arm: add support for TIF_NOTIFY_SIGNAL"). > After the commit, any bit in the range of 0..15 will cause > do_work_pending() to be invoked. More frequent do_work_pending() > invoked possible result in worse performance. > > Some of the tests I've doneļ¼Œ as follows: > lmbench test base with patch > ./lat_ctx -P 1 -s 0 2 7.3167 11.04 > ./lat_ctx -P 1 -s 16 2 8.0467 14.5367 > ./lat_ctx -P 1 -s 64 2 7.8667 11.43 > ./lat_ctx -P 1 -s 16 16 16.47 18.3667 > ./lat_pipe -P 1 28.1671 44.7904 > > libMicro-0.4.1 test base with patch > ./cascade_cond -E -C 200\ > -L -S -W -N "c_cond_1" -I 100 286.3333 358 > > When I adjust test bit, the performance problem gone. > - movs r1, r1, lsl #16 > + ldr r2, =#_TIF_WORK_MASK > + tst r1, r2 > > Does anyone have a good suggestion for this problem? > should just test _TIF_WORK_MASK, as before? I think it should be fine - but I would suggest re-organising the TIF definitions so that those TIF bits that shouldn't trigger do_work_pending are not in the first 16 bits. Note that all four bits in _TIF_SYSCALL_WORK need to stay within an 8-bit even-bit-aligned range, so the value is suitable for an immediate assembly constant. I'd suggest moving the TIF definitions for 20 to 19, and 4..7 to 20..23, and then 8 to 4. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!