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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 03DD2C433FF for ; Wed, 31 Jul 2019 08:46:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3B35206A3 for ; Wed, 31 Jul 2019 08:46:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726817AbfGaIp7 (ORCPT ); Wed, 31 Jul 2019 04:45:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:34062 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725857AbfGaIp7 (ORCPT ); Wed, 31 Jul 2019 04:45:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3337EAE2C; Wed, 31 Jul 2019 08:45:58 +0000 (UTC) Subject: Re: [patch 11/12] hrtimer: Prepare support for PREEMPT_RT To: Paolo Bonzini , Steven Rostedt Cc: Arnaldo Carvalho de Melo , x86@kernel.org, Anna-Maria Gleixner , Sebastian Siewior , Thomas Gleixner , Jiri Olsa , LKML References: <20190726183048.982726647@linutronix.de> <20190726185753.737767218@linutronix.de> <42299f02-ff29-f7e3-45f0-b9fef041aec9@suse.com> <20190729110806.57c57399@gandalf.local.home> <9a9bde89-e0b3-a7b9-749e-a6b35d74b729@redhat.com> From: Juergen Gross Message-ID: <0910bd2b-b5b1-aa41-7f5e-b44f51a516d3@suse.com> Date: Wed, 31 Jul 2019 10:45:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <9a9bde89-e0b3-a7b9-749e-a6b35d74b729@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29.07.19 19:30, Paolo Bonzini wrote: > On 29/07/19 17:08, Steven Rostedt wrote: >> On Sun, 28 Jul 2019 11:06:50 +0200 >> Juergen Gross wrote: >> >>> In case we'd want to change that I'd rather not special case timers, but >>> apply a more general solution to the quite large amount of similar >>> cases: I assume the majority of cpu_relax() uses are affected, so adding >>> a paravirt op cpu_relax() might be appropriate. >>> >>> That could be put under CONFIG_PARAVIRT_SPINLOCK. If called in a guest >>> it could ask the hypervisor to give up the physical cpu voluntarily >>> (in Xen this would be a "yield" hypercall). >> >> Seems paravirt wants our cpu_chill() ;-) > > Actually that is not really a joke! :) As CONFIG_PARAVIRT is no longer so massive intrusive as some time ago it might really be worth thinking of. From Xen perspective I'd really like a way to give up the vcpu instead of doing a busy wait. And having another user and (even better) already some patches addressing some (or all?) callsites sounds like a win-win situation for me. So +1 from me for cpu_chill() via a new paravirt op. Juergen