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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 B8568C433ED for ; Thu, 8 Apr 2021 13:18:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CFDF610CA for ; Thu, 8 Apr 2021 13:18:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230412AbhDHNSn (ORCPT ); Thu, 8 Apr 2021 09:18:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229803AbhDHNSm (ORCPT ); Thu, 8 Apr 2021 09:18:42 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 39CFCC061760 for ; Thu, 8 Apr 2021 06:18:31 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1617887903; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=R3zqpOysd+UgmybGo5NkOd2hIbYM3pm4y3c57K63JxA=; b=ENEhqGLkUvzI55KKXqGU3V8xzhqVR+tPxf5r7dyk9yRRI7SeIJIaN/+DxQ813iDUkmIjLx QXwfKUTPMOCVP+lLCwi17wenWjeNHHO6l84WdKAWYuYBJiwUwZzv1LQJOzGOakQDDII6k/ 4IWVByqdeg1hN8nNAFsSHWR7gdBlaZxiKfGDmLKV89Qoy3lNvtUbpEF6mETNPkEkcgWm6E DvOFMMRkRv7wg4kdTCfOcU5LsnEbWohnbfBICbYQFFufPSfVtr6eWVEKsk/vPBqNfIsZ2p NqdHOEo76isPI7/BVR37NPHtV874x2mo9eGmTgOl7RBLvreRzQJP06y2zrtmRg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1617887903; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=R3zqpOysd+UgmybGo5NkOd2hIbYM3pm4y3c57K63JxA=; b=j0BgA4b2utC5JU1UQGkKE9lOkh/3swaNqVDzrGQ5PbRq2VaxQOjbHjUSPSmzBhoFPBtgM8 5PzstL9LzDhmDHBQ== To: Sean Christopherson , Michael Tokarev Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, Paolo Bonzini Subject: Re: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting In-Reply-To: Date: Thu, 08 Apr 2021 15:18:23 +0200 Message-ID: <874kgg29uo.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Apr 06 2021 at 21:47, Sean Christopherson wrote: > On Tue, Apr 06, 2021, Michael Tokarev wrote: >> broke kvm guest cpu time accounting - after this commit, when running >> qemu-system-x86_64 -enable-kvm, the guest time (in /proc/stat and >> elsewhere) is always 0. >> >> I dunno why it happened, but it happened, and all kernels after 5.9 >> are affected by this. >> >> This commit is found in a (painful) git bisect between kernel 5.8 and 5.10. > > Yes :-( > > There's a bugzilla[1] and two proposed fixes[2][3]. I don't particularly like > either of the fixes, but an elegant solution hasn't presented itself. > > Thomas/Paolo, can you please weigh in? > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=209831 > [2] https://lkml.kernel.org/r/1617011036-11734-1-git-send-email-wanpengli@tencent.com > [3] https://lkml.kernel.org/r/20210206004218.312023-1-seanjc@google.com All of the solutions I looked at so far are ugly as hell. The problem is that the accounting is plumbed into the context tracking and moving context tracking around to a different place is just wrong. I think the right solution is to seperate the time accounting logic out from guest_enter/exit_irqoff() and have virt time specific helpers which can be placed at the proper spots in kvm. Thanks, tglx