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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 D2A6AC5DF60 for ; Thu, 7 Nov 2019 09:13:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 970DC21D82 for ; Thu, 7 Nov 2019 09:13:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jnbLISrU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387619AbfKGJNH (ORCPT ); Thu, 7 Nov 2019 04:13:07 -0500 Received: from merlin.infradead.org ([205.233.59.134]:58662 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727120AbfKGJNH (ORCPT ); Thu, 7 Nov 2019 04:13:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=stpQ2ZxVbR6vwFgf2kbMBwfdaXFgcnuA4lpQdxAozKo=; b=jnbLISrUxo7DzyoIX7Dwgcg8y bC3qwfzYzuye2C2c6PMptTeYRd37Cl7MMcQwjhBnmwbAoB8QmFMjtWZrsx0cZ56o5VBh/NIdwLkgE sIN+e025d509E07PGAEnTAPSCsYJVvQX3UnB0qohMqWKg0qT/tz9QSzRv6/a51yyWtBgDAxAIryGt +u+7tZpXt8B+x8ZmlCq+/gQg+DJoeA3aa6tsjsyHQUuYeWptQeePwdCNJjQetywE6/Pt+bJmGO10r A0h0nttFg5vbtzuXo2I72B8e3mYoumeScnymEIp/LdKPcZaXI46WDVs4ZEzQdJKNomqCh02NNKzsd nsTTLyAOw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iSdqF-0002Xp-Ry; Thu, 07 Nov 2019 09:12:36 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 61933300692; Thu, 7 Nov 2019 10:11:27 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BAC432B13B364; Thu, 7 Nov 2019 10:12:31 +0100 (CET) Date: Thu, 7 Nov 2019 10:12:31 +0100 From: Peter Zijlstra To: Thomas Gleixner Cc: LKML , x86@kernel.org, Stephen Hemminger , Willy Tarreau , Juergen Gross , Sean Christopherson , Linus Torvalds , "H. Peter Anvin" Subject: Re: [patch 4/9] x86/io: Speedup schedule out of I/O bitmap user Message-ID: <20191107091231.GA4131@hirez.programming.kicks-ass.net> References: <20191106193459.581614484@linutronix.de> <20191106202806.133597409@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106202806.133597409@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 06, 2019 at 08:35:03PM +0100, Thomas Gleixner wrote: > There is no requirement to update the TSS I/O bitmap when a thread using it is > scheduled out and the incoming thread does not use it. > > For the permission check based on the TSS I/O bitmap the CPU calculates the memory > location of the I/O bitmap by the address of the TSS and the io_bitmap_base member > of the tss_struct. The easiest way to invalidate the I/O bitmap is to switch the > offset to an address outside of the TSS limit. > > If an I/O instruction is issued from user space the TSS limit causes #GP to be > raised in the same was as valid I/O bitmap with all bits set to 1 would do. > > This removes the extra work when an I/O bitmap using task is scheduled out > and puts the burden on the rare I/O bitmap users when they are scheduled > in. This also nicely aligns with that the context switch time is accounted to the next task. So by doing the expensive part on switch-in gets it all accounted to the task that caused it.