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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 1490DC32792 for ; Thu, 3 Oct 2019 17:19:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3DEB20830 for ; Thu, 3 Oct 2019 17:19:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570123147; bh=ou04+K90P77FEjz3NVJiDUkWPy03xWDaNgpyoEq38D4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=roSEiB2B3LjiINkE62DGTR1gmiMKwxsx3yh0AEf/aKw/2rno6S4KFq2svbLajNGjt atss7ZwKbxEYFwriocNszwflLiQlBpn9kJ56I9tOPqouFQRl3QhIy16QdHvqjPxjhp qUCewFjG6EQZCJFXwF72vLA5sDgsDi79Z4C7GRWw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390363AbfJCRTH (ORCPT ); Thu, 3 Oct 2019 13:19:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:49770 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387531AbfJCQVa (ORCPT ); Thu, 3 Oct 2019 12:21:30 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E529A20865; Thu, 3 Oct 2019 16:21:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570119690; bh=ou04+K90P77FEjz3NVJiDUkWPy03xWDaNgpyoEq38D4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hDp6Q36fTgUooBwpG39/M2SguPfiUsvqmVtOeLIAVxaKdfBig18WAvmlwpG2364mF W/hIb3YSkCNBdnHV/KhCxLcXvHG4mSXCk1UIe9tTPtf3HEMbYXrABub54sfzWvS81I dGBLQoAMAhElYWBcBAm6Qd3AY/hYyjdFFT4pK98c= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , Jinyu Qi , Joerg Roedel , Robin Murphy , Sasha Levin Subject: [PATCH 4.19 118/211] iommu/iova: Avoid false sharing on fq_timer_on Date: Thu, 3 Oct 2019 17:53:04 +0200 Message-Id: <20191003154514.237490697@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191003154447.010950442@linuxfoundation.org> References: <20191003154447.010950442@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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 9a576ae837dcb..da4516fbf5425 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -580,7 +580,9 @@ 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