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,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 2F481C4740A for ; Mon, 9 Sep 2019 10:23:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 05E482089F for ; Mon, 9 Sep 2019 10:23:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="H2AxMfh6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390656AbfIIKXx (ORCPT ); Mon, 9 Sep 2019 06:23:53 -0400 Received: from mail-wm1-f68.google.com ([209.85.128.68]:55833 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390615AbfIIKXv (ORCPT ); Mon, 9 Sep 2019 06:23:51 -0400 Received: by mail-wm1-f68.google.com with SMTP id g207so13144594wmg.5 for ; Mon, 09 Sep 2019 03:23:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=In6xjIv1qvZx6AHWSp+pYmS8Y+YcRx5T9VqtwgDDOao=; b=H2AxMfh6lZl28VuEpAig+Ks6VvS2c/2mZ96FjkKszabA6MyJP9kHbQ1KKprSKyFSmJ mN4OqbigiTeZ3SFvyoAWcicUp+ltfyiVQvI/5E+Fx8g5Lq1/q6CYklfhsHkBRI1QY/MU dETvL5Cke5dXWfEWU3vBj8E8Ij/JfReNOs3Yy/sxO8XIGlENDWstC5iB0Ttzggciw8CK qQ3SjJQjkpCNt+9wSAjQytMKAwbxIbfFWkxX+TPYPFag194n25iWz50I4ChcDlZEEPuv KMYnXYd3ae0OtxC/b7wnIClKjO4keCcC049HzFNRzUbrsnSwkpz05DTvgEmahBkZQunG FCRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=In6xjIv1qvZx6AHWSp+pYmS8Y+YcRx5T9VqtwgDDOao=; b=ZBK8yMmFKPHPrF5mfo6ov59PAbxEsswYlALn4e7gGymP3mRdZDRj1MUTWf0EbQOjjr W9yNmNTnb3tRAglNzyssDMQGDCioITWYx4OHcTdRjuuF4k+qu+jxHZ+HjWa2Pf5U+h4v nqB3t43RvH0Re9NsqxhSvLTz8uhYLjFSPhiqoe/7eolVoH+snnvI45wGGzDF2XYbX3Gj DpE8NJVIhWEjdfjsDKrTobZTiqo7ncQLs5jgE9CFdBLmrF5XDUVQKRyIDa/WTIU5J6dR 4n0FIT4uHZCLxWWDO+ute59GuF8a+gO1V8ZVbldPMCoE9+ZNpHBkmax+Ri6T2WzB3h4L PGSA== X-Gm-Message-State: APjAAAX0ZzZi7HsKwkIiYSp5j7IkDD6JNmqyJ4vxEn9njvO94VWsftv1 E0G8UJz5zSJiwto1mNbokC0OxjlOrENPUQ== X-Google-Smtp-Source: APXvYqwodAb2hSbu1oBC3qnGuQjKRAYFo/bkD32ISS9HPSjmr8FMWLHhger1WxXkvavqQkINxe6skw== X-Received: by 2002:a7b:c5ca:: with SMTP id n10mr18393828wmk.138.1568024629199; Mon, 09 Sep 2019 03:23:49 -0700 (PDT) Received: from Mindolluin.localdomain ([148.69.85.38]) by smtp.gmail.com with ESMTPSA id d14sm1800008wrj.27.2019.09.09.03.23.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Sep 2019 03:23:48 -0700 (PDT) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Adrian Reber , Alexander Viro , Andrei Vagin , Andy Lutomirski , Cyrill Gorcunov , Ingo Molnar , Oleg Nesterov , Pavel Emelyanov , Thomas Gleixner , containers@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 4/9] select: Micro-optimise __estimate_accuracy() Date: Mon, 9 Sep 2019 11:23:35 +0100 Message-Id: <20190909102340.8592-5-dima@arista.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190909102340.8592-1-dima@arista.com> References: <20190909102340.8592-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Shift on s64 is faster than division, use it instead. As the result of the patch there is a hardly user-visible effect: poll(), select(), etc syscalls will be a bit more precise on ~2.3% than before because 1000 != 1024 :) Signed-off-by: Dmitry Safonov --- fs/select.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/fs/select.c b/fs/select.c index 12cdefd3be2d..2477c202631e 100644 --- a/fs/select.c +++ b/fs/select.c @@ -51,15 +51,14 @@ static long __estimate_accuracy(ktime_t slack) { - int divfactor = 1000; - if (slack < 0) return 0; - if (task_nice(current) > 0) - divfactor = divfactor / 5; + /* A bit more precise than 0.1% */ + slack = slack >> 10; - slack = ktime_divns(slack, divfactor); + if (task_nice(current) > 0) + slack = slack * 5; if (slack > MAX_SLACK) return MAX_SLACK; -- 2.23.0