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=-17.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham 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 158F9C3A5A1 for ; Wed, 28 Aug 2019 13:13:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D32102070B for ; Wed, 28 Aug 2019 13:13:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="krpjyvPl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726738AbfH1NNo (ORCPT ); Wed, 28 Aug 2019 09:13:44 -0400 Received: from mail-vs1-f74.google.com ([209.85.217.74]:37799 "EHLO mail-vs1-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726253AbfH1NNn (ORCPT ); Wed, 28 Aug 2019 09:13:43 -0400 Received: by mail-vs1-f74.google.com with SMTP id r17so481375vsp.4 for ; Wed, 28 Aug 2019 06:13:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=2uraJyf6YkQQQi+GjgA0Euznea67jY0h3NcNTgfEE6E=; b=krpjyvPl4LV2Qp+9bxrX89f65tIa90HGC+HFV5rCeRCZ2Kify9kiCPez94yN8srqEe lF+iaLa/UcZn4j756/FDjGcCZ0fi4GAImCz5nAKjfHbDVT4WihMlJOA0Oqe8/oU0YGwb Ld33DNMmuOqncMmBjsxdkFdvO20z+TkgT4PefRIYKIBpXFcXzihDFcx0+HYRLWrzVt0z Y7v7VnMqtFJ/H51CNlWRxy/3Fa6SCQyge9Dfc/AvqyjN+8IBUTQoqfTpv9OXaM4uCDMu tTEYpdiWaBNUKVP37xirxcot4wu+OthQfooyIBAkDMtVrRe6c9qMKF2yFsg7vRx5S76T eOQg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=2uraJyf6YkQQQi+GjgA0Euznea67jY0h3NcNTgfEE6E=; b=QVMhtTreubGrX7LW063iXGJmkeKONvjrbHlInZqeXPXLYMnjCUDzpymzB6lqxxOBIG Vz2zRQw/TOhTwMyc0/SdZ/hEuVp8D5BML7Qoi/6fSPATCGd/W4Pkm7nB+2ZG5+p4cUut uOpL9g7wEbEnGtjb0+09Va7tQ/c7ck4uqYCZdQZHHV/7YKkbiXwBpaBVWsjMDwrKcbpC LPK09noAmUINhVSQmBY+nWJn8/wXeKsQU3t4cDVjn1+ezZSp3jsGJZ2PQbb/wWCfoVGL UNY8gg1XDGcq+2WAaP7Idp0F2fa+rXc560UZzf3dRy4JHKpJuEnX52wuQoTWCd3Ov1UH OHpA== X-Gm-Message-State: APjAAAVXl1LOO24YnpzMFezkXVYQGETBqM93g6ZzNtPoDk9H/ETw4PiM 3GolDK2U42TOgr4qJTwI2LV3jogrZ8O1Gg== X-Google-Smtp-Source: APXvYqxwaE69Ih/IcaBEjoZYAtqpyYGYen7SRacn6ADCDqJa8PItgJpR3VuZvxi6a1jkwLHNsHIcq0P0fvxZJQ== X-Received: by 2002:a67:d02:: with SMTP id 2mr2090357vsn.43.1566998022308; Wed, 28 Aug 2019 06:13:42 -0700 (PDT) Date: Wed, 28 Aug 2019 06:13:38 -0700 Message-Id: <20190828131338.89832-1-edumazet@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.23.0.187.g17f5b7556c-goog Subject: [PATCH] iommu/iova: avoid false sharing on fq_timer_on From: Eric Dumazet To: Joerg Roedel Cc: linux-kernel , iommu@lists.linux-foundation.org, Eric Dumazet , Eric Dumazet , Jinyu Qi Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Jinyu Qi Cc: Joerg Roedel --- 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 3e1a8a6755723a927a7942a7429ab7e6c19a0027..41c605b0058f9615c2dbdd83f1de2404a9b1d255 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)); } -- 2.23.0.187.g17f5b7556c-goog