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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 E2640C3A5A2 for ; Fri, 20 Sep 2019 23:39:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABBEA218AE for ; Fri, 20 Sep 2019 23:39:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569022776; bh=4HiXLY7SR+iAroiaABOE6W7gGGt/ONbMyy8ANXwOep4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=lM2XQmnkRiWl+VpvdrqCsVftLTFoIVatMl1O4IdL1WcqE6UwoQLnHvPKoBdIJCgws k+0lPM0+rttOgh4jYKjNiEvqv77u+oNJcW/NLPl8NmmiFsDJ/KI/dAOnNjVaHzuSfs mtR9K3CLLQ/S9M9e47aAew/BtT2BWvJptq6HLOXQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407171AbfITXjf (ORCPT ); Fri, 20 Sep 2019 19:39:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:47758 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404477AbfITXjf (ORCPT ); Fri, 20 Sep 2019 19:39:35 -0400 Received: from mail-wr1-f47.google.com (mail-wr1-f47.google.com [209.85.221.47]) (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 C76E52086A for ; Fri, 20 Sep 2019 23:39:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569022775; bh=4HiXLY7SR+iAroiaABOE6W7gGGt/ONbMyy8ANXwOep4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=TiaMcIuGGLxPrOEAFlEHFcZlY+qvCuwR3Tv5RLwWD12MBqXhwYI4rAlcBvKkqj3qs P8rZaAUJJJvXe77eDw6atNAmSYg0RqipnbylR3+On+Ls/n6RkFVJkoCND2qw8Jkk4C EBENG9ZdejpTO41gWG6PlV2mrNmYgU3hurWjUSbw= Received: by mail-wr1-f47.google.com with SMTP id b9so8390191wrs.0 for ; Fri, 20 Sep 2019 16:39:34 -0700 (PDT) X-Gm-Message-State: APjAAAXv7Sw6PL/RwFYmMbXjHrZhIVCqayo2C/7zeWWuMKxlrM2MhQyf EY912N5Xik+J2rwdTExBhxbSqnKrih8v2RZpYMX9lw== X-Google-Smtp-Source: APXvYqyttEaTBTtUv9CZjWf1dwnYpF+MAvwz70YHeSpaqrhzWfqT5ojsq0XrDIeFVEc/vxF0bimTJcWEcxSbUxwu+7o= X-Received: by 2002:a5d:4c92:: with SMTP id z18mr12990388wrs.111.1569022773387; Fri, 20 Sep 2019 16:39:33 -0700 (PDT) MIME-Version: 1.0 References: <20190919150314.054351477@linutronix.de> <20190919150808.617944343@linutronix.de> In-Reply-To: <20190919150808.617944343@linutronix.de> From: Andy Lutomirski Date: Fri, 20 Sep 2019 16:39:22 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC patch 02/15] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY To: Thomas Gleixner Cc: LKML , X86 ML , Peter Zijlstra , Andy Lutomirski , Catalin Marinas , Will Deacon , Mark Rutland , Marc Zyngier , Paolo Bonzini , kvm list , linux-arch 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 On Thu, Sep 19, 2019 at 8:09 AM Thomas Gleixner wrote: > > Evaluating _TIF_NOHZ to decide whether to use the slow syscall entry path > is not only pointless, it's actually counterproductive: > > 1) Context tracking code is invoked unconditionally before that flag is > evaluated. > > 2) If the flag is set the slow path is invoked for nothing due to #1 Can we also get rid of TIF_NOHZ on x86?