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=-7.2 required=3.0 tests=DATE_IN_PAST_06_12, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C2FDDC10F26 for ; Fri, 6 Mar 2020 19:52:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F95E20656 for ; Fri, 6 Mar 2020 19:52:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K0J4Fj87" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726307AbgCFTwR (ORCPT ); Fri, 6 Mar 2020 14:52:17 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:53444 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726083AbgCFTwQ (ORCPT ); Fri, 6 Mar 2020 14:52:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583524335; 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:references:references; bh=7wshUEfGJ0oCbRrCm+psHycgVdvMv8N6eiO1mp9WFHQ=; b=K0J4Fj875O1K8xDURpjSaDB+NNNWgB35W5dA+RRKec/DZjhiJAeLRvMbc8hHcCqGaXJqrn fvgYKGbNUeGMecJmbGzQQVYAeLg3tN5Mw2QJUnnpvYVOVczo8Kn/lZEqurR8pCNUoCfOg6 GnmQwijqUGUa9CvKaPL9l7MddGY/UD0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-235-ZbozAVvCPia2fE25-rWBtQ-1; Fri, 06 Mar 2020 14:52:13 -0500 X-MC-Unique: ZbozAVvCPia2fE25-rWBtQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F2F7F800053; Fri, 6 Mar 2020 19:52:11 +0000 (UTC) Received: from fuller.cnet (ovpn-116-16.gru2.redhat.com [10.97.116.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6295B10027AB; Fri, 6 Mar 2020 19:52:11 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 2562842FE410; Fri, 6 Mar 2020 06:56:17 -0300 (-03) Date: Fri, 6 Mar 2020 06:56:17 -0300 From: Marcelo Tosatti To: "Maciej S. Szmigiero" , Paolo Bonzini Cc: "Rafael J. Wysocki" , Daniel Lezcano , Joao Martins , Boris Ostrovsky , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] cpuidle-haltpoll: allow force loading on hosts without the REALTIME hint Message-ID: <20200306095617.GD32190@fuller.cnet> References: <20200221174331.1480468-1-mail@maciej.szmigiero.name> <114f7b8d-6f88-222a-d1fa-abcfc0e6a1f2@maciej.szmigiero.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <114f7b8d-6f88-222a-d1fa-abcfc0e6a1f2@maciej.szmigiero.name> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Feb 24, 2020 at 09:10:18PM +0100, Maciej S. Szmigiero wrote: > (CC'ing also Marcelo as the cpuidle-haltpoll driver author and the KVM ML). Hi Maciej, > On 21.02.2020 18:43, Maciej S. Szmigiero wrote: > > From: "Maciej S. Szmigiero" > > > > Before commit 1328edca4a14 ("cpuidle-haltpoll: Enable kvm guest polling > > when dedicated physical CPUs are available") the cpuidle-haltpoll driver > > could also be used in scenarios when the host does not advertise the > > KVM_HINTS_REALTIME hint. > > > > While the behavior introduced by the aforementioned commit makes sense as > > the default It makes sense for the pCPU overcommitted case only. > > there are cases where the old behavior is desired, for example, > > when other kernel changes triggered by presence by this hint are unwanted, > > for some workloads where the latency benefit from polling overweights the > > loss from idle CPU capacity that otherwise would be available, or just when > > running under older Qemu versions that lack this hint. > > > > Let's provide a typical "force" module parameter that allows restoring the > > old behavior. > > > > Signed-off-by: Maciej S. Szmigiero I would rather: 1) Switch back to the default non-overcommitted case. or even better (but requires more investment) 2) Make on the flight dynamic configuration (after all pCPU overcommitment=true/false is a property that changes during the day, depending on system load). But its up to Paolo to decide, really. > > --- > > drivers/cpuidle/cpuidle-haltpoll.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c > > index b0ce9bc78113..07e5b36076bb 100644 > > --- a/drivers/cpuidle/cpuidle-haltpoll.c > > +++ b/drivers/cpuidle/cpuidle-haltpoll.c > > @@ -18,6 +18,11 @@ > > #include > > #include > > > > +static bool force __read_mostly; > > +module_param(force, bool, 0444); > > +MODULE_PARM_DESC(force, > > + "Load even if the host does not provide the REALTIME hint"); > > + > > static struct cpuidle_device __percpu *haltpoll_cpuidle_devices; > > static enum cpuhp_state haltpoll_hp_state; > > > > @@ -90,6 +95,11 @@ static void haltpoll_uninit(void) > > haltpoll_cpuidle_devices = NULL; > > } > > > > +static bool haltpool_want(void) > > +{ > > + return kvm_para_has_hint(KVM_HINTS_REALTIME) || force; > > +} > > + > > static int __init haltpoll_init(void) > > { > > int ret; > > @@ -102,7 +112,7 @@ static int __init haltpoll_init(void) > > cpuidle_poll_state_init(drv); > > > > if (!kvm_para_available() || > > - !kvm_para_has_hint(KVM_HINTS_REALTIME)) > > + !haltpool_want()) > > return -ENODEV; > > > > ret = cpuidle_register_driver(drv); > >