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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 C4F76C3A5A6 for ; Sun, 22 Sep 2019 18:53:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 95C0E21D7B for ; Sun, 22 Sep 2019 18:53:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569178419; bh=9SO459Tx95hQLcr6M3fZdhK5p3dMn/Dz2ldcdyi20Qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=BPmazwAk5bULRc2XVwzQQ2VfD5EzIjYzG+7/oigxk/jZNmdxLpOAEJzg+6gguV989 m7Oqzyzk+8cXxxD/RrzGRvQ+bgT1+I4BwJzFQxLTG5E5eS28/0uSNaIa7/mD9RXIdY LImklEyn6XlWspWdxCnOs6kPF1g0jRSacsaqngB4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394355AbfIVSxi (ORCPT ); Sun, 22 Sep 2019 14:53:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:52808 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393614AbfIVSxN (ORCPT ); Sun, 22 Sep 2019 14:53:13 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7197E21D79; Sun, 22 Sep 2019 18:53:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569178392; bh=9SO459Tx95hQLcr6M3fZdhK5p3dMn/Dz2ldcdyi20Qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y0kb8t8cso9QRkDSS5PvuCLEbeGnak6pvLrqn6w5+VkAlSgP83iKdUHXaSdG2en8Z WhOJwQYSpdY9XX1aFiCcHUopKBKmdZKWAuhmfFsxadMMn82HXSEjRP4BH/K64bRAn3 tkMAvvvJ6FntjyydQfN2KRlPqFIIjOpCcBsQSln4= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Eric Dumazet , Jinyu Qi , Joerg Roedel , Robin Murphy , Sasha Levin , iommu@lists.linux-foundation.org Subject: [PATCH AUTOSEL 5.2 138/185] iommu/iova: Avoid false sharing on fq_timer_on Date: Sun, 22 Sep 2019 14:48:36 -0400 Message-Id: <20190922184924.32534-138-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190922184924.32534-1-sashal@kernel.org> References: <20190922184924.32534-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Dumazet [ Upstream commit 0d87308cca2c124f9bce02383f1d9632c9be89c4 ] In commit 14bd9a607f90 ("iommu/iova: Separate atomic variables to improve performance") Jinyu Qi identified that the atomic_cmpxchg() in queue_iova() was causing a performance loss and moved critical fields so that the false sharing would not impact them. However, avoiding the false sharing in the first place seems easy. We should attempt the atomic_cmpxchg() no more than 100 times per second. Adding an atomic_read() will keep the cache line mostly shared. This false sharing came with commit 9a005a800ae8 ("iommu/iova: Add flush timer"). Signed-off-by: Eric Dumazet Fixes: 9a005a800ae8 ('iommu/iova: Add flush timer') Cc: Jinyu Qi Cc: Joerg Roedel Acked-by: Robin Murphy Signed-off-by: Joerg Roedel Signed-off-by: Sasha Levin --- drivers/iommu/iova.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 3e1a8a6755723..41c605b0058f9 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -577,7 +577,9 @@ void queue_iova(struct iova_domain *iovad, spin_unlock_irqrestore(&fq->lock, flags); - if (atomic_cmpxchg(&iovad->fq_timer_on, 0, 1) == 0) + /* Avoid false sharing as much as possible. */ + if (!atomic_read(&iovad->fq_timer_on) && + !atomic_cmpxchg(&iovad->fq_timer_on, 0, 1)) mod_timer(&iovad->fq_timer, jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); } -- 2.20.1