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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78F0DC4332F for ; Fri, 1 Oct 2021 16:42:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63F2C61A63 for ; Fri, 1 Oct 2021 16:42:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232131AbhJAQns (ORCPT ); Fri, 1 Oct 2021 12:43:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56916 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232109AbhJAQns (ORCPT ); Fri, 1 Oct 2021 12:43:48 -0400 Received: from mail-qk1-x735.google.com (mail-qk1-x735.google.com [IPv6:2607:f8b0:4864:20::735]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF650C061775 for ; Fri, 1 Oct 2021 09:42:03 -0700 (PDT) Received: by mail-qk1-x735.google.com with SMTP id d207so9806916qkg.0 for ; Fri, 01 Oct 2021 09:42:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=aQbL8pXIXocxX9H8b/2nNpVZyCyOOEJ+2eX3f4bQsb0=; b=wXbQCGjvp4GLHV24dvNcEoftO+b+jxKTmz0SX5x2HR0+WKCJvkioVyd5rDUb2pCsyj o4MwxX88vRap3XoIMPH26Rln/IMU3v7eS9oXh7nMXv+ICLXwXcGBr6pwdAR2E1rH+e9G KNiwnEpz/fBuGfOjg9/YJkFPWP0jIasbrHIi5xoe9Jmc2rwoK0LDzR/wU1wjZbeFmvdD YEhrospe7J6JtzCADzrRF55UOLO4nVmGg2KvlI4Zwe+SSleJ/yccWHSdHTqccQETU7z8 JuQIl058Sfvctk3JRr/BoFuVNjJ4FsVaTDrdfRW23LqaJ1v9W9MoKhc5ea1v1Qa+zBz4 WCMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=aQbL8pXIXocxX9H8b/2nNpVZyCyOOEJ+2eX3f4bQsb0=; b=zQMZKMC+eNMx6BQp+tl9Wjf3c5xMg79AIY4Oyxk8UJooSfSrXtpGiMBjYyLNlESyzZ YFooUQ956U8rwkCLJ3ZtUkREsPTjbGGGayBEx9n6nXcZuNnDiFQb69A1X97xDASZHb8b pO5gX1/DJxxIUZQWPunMeouvVTdsTeIjo/OYSenL+RIZhiYYYEARaxLwMbrKggAP1ohT FspnWmK+7RJ7i0fFQ8qM6A66VPAZS/8HJKubA1Vg6+MAvSJWguYFyIkIPWsgoBMvhFSW tvAVFYTPXcWKQkausSNNoIb/nNs4m4taX+eS8U6OFGCOlAr5JQyYiaOZHc3Bo46udqeb fQaw== X-Gm-Message-State: AOAM5312wpFC+sd6Rvx5WCIZjxCcYF63n8cJixwffOi720h7AYwtmwb3 +mwoh2/UvwG6j1JggK+LgePEmA== X-Google-Smtp-Source: ABdhPJxEISaAeFeyVBnUq/DuWLEI7heMQCiSZdmm/c7At99cOYDg6yzkNykzMscChFIJiV2TCPFeTA== X-Received: by 2002:ae9:eb58:: with SMTP id b85mr10034928qkg.323.1633106522896; Fri, 01 Oct 2021 09:42:02 -0700 (PDT) Received: from [192.168.3.43] (c-67-174-166-185.hsd1.ga.comcast.net. [67.174.166.185]) by smtp.gmail.com with ESMTPSA id p12sm3298438qkj.54.2021.10.01.09.42.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Oct 2021 09:42:02 -0700 (PDT) Subject: Re: [RFC PATCH 00/13] x86 User Interrupts support To: Stefan Hajnoczi , Sohil Mehta , Peter Maydell , =?UTF-8?Q?Alex_Benn=c3=a9e?= Cc: Andy Lutomirski , the arch/x86 maintainers , Tony Luck , Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jens Axboe , Christian Brauner , "Peter Zijlstra (Intel)" , Shuah Khan , Arnd Bergmann , Jonathan Corbet , Raj Ashok , Jacob Pan , Gayatri Kammela , Zeng Guang , "Williams, Dan J" , Randy E Witt , "Shankar, Ravi V" , Ramesh Thomas , Linux API , linux-arch@vger.kernel.org, Linux Kernel Mailing List , linux-kselftest@vger.kernel.org, qemu-devel@nongnu.org References: <20210913200132.3396598-1-sohil.mehta@intel.com> <456bf9cf-87b8-4c3d-ac0c-7e392bcf26de@www.fastmail.com> <778d40fe-ad8e-fd7c-4caa-499910bb0925@intel.com> From: Richard Henderson Message-ID: <3abdadab-9b7e-7cc0-5ec5-17fa385ce7d4@linaro.org> Date: Fri, 1 Oct 2021 12:41:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 10/1/21 12:35 PM, Stefan Hajnoczi wrote: > QEMU's TCG threads execute translated code. There are events that > require interrupting these threads. Today a check is performed at the > start of every translated block. Most of the time the check is false and > it's a waste of CPU. > > User interrupts can eliminate the need for checks by interrupting TCG > threads when events occur. We used to use interrupts, and stopped because we need to wait until the guest is in a stable state. The guest is always in a stable state at the beginning of each TB. See 378df4b2375. r~