From patchwork Tue Oct 6 17:46:30 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 7338801 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 291689F1D5 for ; Tue, 6 Oct 2015 17:49:53 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 4365B2060E for ; Tue, 6 Oct 2015 17:49:52 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3F7DA205ED for ; Tue, 6 Oct 2015 17:49:51 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZjWKo-0008N1-8I; Tue, 06 Oct 2015 17:47:30 +0000 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZjWKF-0007pO-Af for linux-arm-kernel@lists.infradead.org; Tue, 06 Oct 2015 17:46:57 +0000 Received: from edgewater-inn.cambridge.arm.com (edgewater-inn.cambridge.arm.com [10.1.203.122]) by cam-admin0.cambridge.arm.com (8.12.6/8.12.6) with ESMTP id t96HkVWx001365; Tue, 6 Oct 2015 18:46:32 +0100 (BST) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id BDD711AE0E5B; Tue, 6 Oct 2015 18:46:32 +0100 (BST) From: Will Deacon To: catalin.marinas@arm.com Subject: [PATCH v2 10/10] arm64: mm: remove dsb from update_mmu_cache Date: Tue, 6 Oct 2015 18:46:30 +0100 Message-Id: <1444153590-24173-11-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1444153590-24173-1-git-send-email-will.deacon@arm.com> References: <1444153590-24173-1-git-send-email-will.deacon@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20151006_104655_863204_C62F27D8 X-CRM114-Status: GOOD ( 10.54 ) X-Spam-Score: -6.9 (------) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Will Deacon , linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP update_mmu_cache() consists of a dsb(ishst) instruction so that new user mappings are guaranteed to be visible to the page table walker on exception return. In reality this can be a very expensive operation which is rarely needed. Removing this barrier shows a modest improvement in hackbench scores and , in the worst case, we re-take the user fault and establish that there was nothing to do. Reviewed-by: Catalin Marinas Signed-off-by: Will Deacon --- arch/arm64/include/asm/pgtable.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 26b066690593..0d18e88e1cfa 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -646,10 +646,10 @@ static inline void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) { /* - * set_pte() does not have a DSB for user mappings, so make sure that - * the page table write is visible. + * We don't do anything here, so there's a very small chance of + * us retaking a user fault which we just fixed up. The alternative + * is doing a dsb(ishst), but that penalises the fastpath. */ - dsb(ishst); } #define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)