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=-10.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 9D8FBC433ED for ; Wed, 14 Apr 2021 10:43:40 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 5336C6100B for ; Wed, 14 Apr 2021 10:43:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5336C6100B Authentication-Results: mail.kernel.org; dmarc=fail (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=desiato.20200630; h=Sender:Content-Transfer-Encoding :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-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=nipws032c+XlHFMcEk5FZdxnv3JGiZu4RnDy0eFpXPE=; b=b3Qz9BXxT1Tn6R61xzPsL2QVm fZ4Y+7bwfe9pAB3vheNoAXNuvJ74JsyMyKNrWUMnhERYQAmDFKAg1VmsbUrLtHnXU2oK2TTvNYaKj Z/8VNBPZE0AA7s/7lljti/phR19C8/iy6EFr+UAPlw7EY/8jIj7Savi8+KkHynSD1xfFG8BS+GyAw gNra9geS6Zbe8Blu2NhC/pWYZbTiuabnIL/s1GFhxL7wdZ1uD1R1dZf675fUDjm7jzCR5lc8j5hr+ TTWAkwfgIX3Q71uJ9gA4cvncO7CWhIA91JG++YZsT51EwE8evBGSDE9bPRFspLtBTJ0gCy9thnGoW 3vbyhTIIw==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lWcy7-00CIp4-Hu; Wed, 14 Apr 2021 10:41:59 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lWcy1-00CIof-Uh for linux-arm-kernel@desiato.infradead.org; Wed, 14 Apr 2021 10:41:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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; bh=1TLhDIimCJ+0/OMhi/q+B1jp80s5VWeBATSEcinNS/8=; b=mnC/D8xgWmU0n+/O4f8PkF+Ov7 KX7UzY9DtBisbS8ByRVIi+R59S2g4RfSKmFC9FFyiwNyh0jIu2rnSk3JlVTrlWE+LHevCrmUo2KVA K7fuH82r/SsRNj53JIvp+/CEf7WOpnveGguHKMrV4Lz+ZpITvfaSNxHojGlxqjgi2KqsENT9CxwMJ ROVyN8T3qBc4KB91Bfp0POFnB+61H0jnhGtMqciADaNND/DlBXEc2Atmzw982eALK7MLsuYV4r53W WvfRal12570lZL3e5IM9ijKkkfxBT/aQ54/ce64rZdB0/NhFNVAwXPzEp33VbbRUA2SnoGGcsb0Le CLx0wcRg==; Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lWcxz-007gh4-Dp for linux-arm-kernel@lists.infradead.org; Wed, 14 Apr 2021 10:41:52 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 053D660E09; Wed, 14 Apr 2021 10:41:46 +0000 (UTC) Date: Wed, 14 Apr 2021 11:41:44 +0100 From: Catalin Marinas To: Kai Shen Cc: will@kernel.org, linux-arm-kernel@lists.infradead.org, LKML , xuwei5@hisilicon.com, hewenliang4@huawei.com, wuxu.wu@huawei.com Subject: Re: [PATCH] arm64:align function __arch_clear_user Message-ID: <20210414104144.GB8320@arm.com> References: <58fecb22-f932-cb6e-d996-ca75fe26a75d@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <58fecb22-f932-cb6e-d996-ca75fe26a75d@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210414_034151_505112_25DCD381 X-CRM114-Status: GOOD ( 16.19 ) 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: 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, Apr 14, 2021 at 05:25:43PM +0800, Kai Shen wrote: > Performance decreases happen in __arch_clear_user when this > function is not correctly aligned on HISI-HIP08 arm64 SOC which > fetches 32 bytes (8 instructions) from icache with a 32-bytes > aligned end address. As a result, if the hot loop is not 32-bytes > aligned, it may take more icache fetches which leads to decrease > in performance. > Dump of assembler code for function __arch_clear_user: > 0xffff0000809e3f10 : nop > 0xffff0000809e3f14 : mov x2, x1 > 0xffff0000809e3f18 : subs x1, x1, #0x8 > 0xffff0000809e3f1c : b.mi 0xffff0000809e3f30 <__arch_clear_user+3 > ----- 0xffff0000809e3f20 : str xzr, [x0],#8 > hot 0xffff0000809e3f24 : nop > loop 0xffff0000809e3f28 : subs x1, x1, #0x8 > ----- 0xffff0000809e3f2c : b.pl 0xffff0000809e3f20 <__arch_clear_user+1 > The hot loop above takes one icache fetch as the code is in one > 32-bytes aligned area and the loop takes one more icache fetch > when it is not aligned like below. > 0xffff0000809e4178 : str xzr, [x0],#8 > 0xffff0000809e417c : nop > 0xffff0000809e4180 : subs x1, x1, #0x8 > 0xffff0000809e4184 : b.pl 0xffff0000809e4178 <__arch_clear_user+ > Data collected by perf: > aligned not aligned > instructions 57733790 57739065 > L1-dcache-store 14938070 13718242 > L1-dcache-store-misses 349280 349869 > L1-icache-loads 15380895 28500665 > As we can see, L1-icache-loads almost double when the loop is not > aligned. > This problem is found in linux 4.19 on HISI-HIP08 arm64 SOC. > Not sure what the case is on other arm64 SOC, but it should do > no harm. > Signed-off-by: Kai Shen Do you have a real world workload that's affected by this function? I'm against adding alignments and nops for specific hardware implementations. What about lots of other loops that the compiler may generate or that we wrote in asm? -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel