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,URIBL_BLOCKED,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 AED7BC3A5A2 for ; Sun, 22 Sep 2019 19:10:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E995206C2 for ; Sun, 22 Sep 2019 19:10:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569179403; bh=VnqvqDmvLnPRno+IQHcRkrnyttl/4Ef4BywZuABrN5A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=j2jlyhKQK1zEAptAZ5+9aak45eARDZWOTcklkJWLfFjRs0jmodPM2wb04v5aGk0om P46dvwMbMMYb/WO//1VMkDQ7R49LajBpjMvSfZA7srg+ywV3uiROSrh5T6cu7p6Onu u10yqYKmXpK1yLlxef5uB4clELsRSWXp4hGah+sA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393768AbfIVTKC (ORCPT ); Sun, 22 Sep 2019 15:10:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:33820 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394968AbfIVS65 (ORCPT ); Sun, 22 Sep 2019 14:58:57 -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 3EE5D2186A; Sun, 22 Sep 2019 18:58:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569178737; bh=VnqvqDmvLnPRno+IQHcRkrnyttl/4Ef4BywZuABrN5A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K8mPJnL/KopQYUOOsJBIT4nm0+rYLW2oWZMfxQs+BDyS1HVoGNT+UeeeGgx3afptz ZvSGCHNOXwf2Nlozbq9vhd3ekt1dX1Q0dEjFQrhin09Osn7bjVlVneVUlE91G5DB5D NF81qmCvJ+EbcSJ9FObMnpd9u816ev4HQPeY8JJ0= 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 4.14 65/89] iommu/iova: Avoid false sharing on fq_timer_on Date: Sun, 22 Sep 2019 14:56:53 -0400 Message-Id: <20190922185717.3412-65-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190922185717.3412-1-sashal@kernel.org> References: <20190922185717.3412-1-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 9f35b9a0d6d86..4edf65dbbcab5 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -607,7 +607,9 @@ 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