From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752302AbdGDOxn (ORCPT ); Tue, 4 Jul 2017 10:53:43 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:48827 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752179AbdGDOxl (ORCPT ); Tue, 4 Jul 2017 10:53:41 -0400 Date: Tue, 4 Jul 2017 16:50:54 +0200 (CEST) From: Thomas Gleixner To: =?ISO-8859-2?Q?Radim_Kr=E8m=E1=F8?= cc: Yang Zhang , Paolo Bonzini , Wanpeng Li , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Jonathan Corbet , tony.luck@intel.com, Borislav Petkov , Peter Zijlstra , mchehab@kernel.org, Andrew Morton , krzk@kernel.org, jpoimboe@redhat.com, Andy Lutomirski , Christian Borntraeger , Thomas Garnier , Robert Gerst , Mathias Krause , douly.fnst@cn.fujitsu.com, Nicolai Stange , Frederic Weisbecker , dvlasenk@redhat.com, Daniel Bristot de Oliveira , yamada.masahiro@socionext.com, mika.westerberg@linux.intel.com, Chen Yu , aaron.lu@intel.com, Steven Rostedt , Kyle Huey , Len Brown , Prarit Bhargava , hidehiro.kawai.ez@hitachi.com, fengtiantian@huawei.com, pmladek@suse.com, jeyu@redhat.com, Larry.Finger@lwfinger.net, zijun_hu@htc.com, luisbg@osg.samsung.com, johannes.berg@intel.com, niklas.soderlund+renesas@ragnatech.se, zlpnobody@gmail.com, Alexey Dobriyan , fgao@48lvckh6395k16k5.yundunddos.com, ebiederm@xmission.com, Subash Abhinov Kasiviswanathan , Arnd Bergmann , Matt Fleming , Mel Gorman , "linux-kernel@vger.kernel.org" , linux-doc@vger.kernel.org, linux-edac@vger.kernel.org, kvm Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll In-Reply-To: <20170704141322.GC30880@potion> Message-ID: References: <4444ffc8-9e7b-5bd2-20da-af422fe834cc@redhat.com> <2245bef7-b668-9265-f3f8-3b63d71b1033@gmail.com> <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> <20170627134043.GA1487@potion> <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com> <20170627142251.GB1487@potion> <20170704141322.GC30880@potion> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: multipart/mixed; BOUNDARY="8323329-169293439-1499179855=:9000" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-169293439-1499179855=:9000 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: 8BIT On Tue, 4 Jul 2017, Radim Krèmáø wrote: > I think there is a nicer solution to avoid the expensive timer rewrite: > Linux uses one-shot APIC timers and getting the timer interrupt is about > as expensive as programming the timer, so the guest can keep the timer > armed, but not re-arm it after the expiration if the CPU is idle. So much for the theory. The NOHZ logic has to reprogram the timer when the next expiry is farther away than the next tick. Otherwise you wake up on every idle entry once for nothing, which defeats the whole purpose of NOHZ to not do that. Thanks, tglx --8323329-169293439-1499179855=:9000-- From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: [2/2] x86/idle: use dynamic halt poll From: Thomas Gleixner Message-Id: Date: Tue, 4 Jul 2017 16:50:54 +0200 (CEST) To: =?ISO-8859-2?Q?Radim_Kr=E8m=E1=F8?= Cc: Yang Zhang , Paolo Bonzini , Wanpeng Li , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Jonathan Corbet , tony.luck@intel.com, Borislav Petkov , Peter Zijlstra , mchehab@kernel.org, Andrew Morton , krzk@kernel.org, jpoimboe@redhat.com, Andy Lutomirski , Christian Borntraeger , Thomas Garnier , Robert Gerst , Mathias Krause , douly.fnst@cn.fujitsu.com, Nicolai Stange , Frederic Weisbecker , dvlasenk@redhat.com, Daniel Bristot de Oliveira , yamada.masahiro@socionext.com, mika.westerberg@linux.intel.com, Chen Yu , aaron.lu@intel.com, Steven Rostedt , Kyle Huey , Len Brown , Prarit Bhargava , hidehiro.kawai.ez@hitachi.com, fengtiantian@huawei.com, pmladek@suse.com, jeyu@redhat.com, Larry.Finger@lwfinger.net, zijun_hu@htc.com, luisbg@osg.samsung.com, johannes.berg@intel.com, niklas.soderlund+renesas@ragnatech.se, zlpnobody@gmail.com, Alexey Dobriyan , fgao@ikuai8.com, ebiederm@xmission.com, Subash Abhinov Kasiviswanathan , Arnd Bergmann , Matt Fleming , Mel Gorman , "linux-kernel@vger.kernel.org" , linux-doc@vger.kernel.org, linux-edac@vger.kernel.org, kvm List-ID: T24gVHVlLCA0IEp1bCAyMDE3LCBSYWRpbSBLcsSNbcOhxZkgd3JvdGU6Cj4gSSB0aGluayB0aGVy ZSBpcyBhIG5pY2VyIHNvbHV0aW9uIHRvIGF2b2lkIHRoZSBleHBlbnNpdmUgdGltZXIgcmV3cml0 ZToKPiBMaW51eCB1c2VzIG9uZS1zaG90IEFQSUMgdGltZXJzIGFuZCBnZXR0aW5nIHRoZSB0aW1l ciBpbnRlcnJ1cHQgaXMgYWJvdXQKPiBhcyBleHBlbnNpdmUgYXMgcHJvZ3JhbW1pbmcgdGhlIHRp bWVyLCBzbyB0aGUgZ3Vlc3QgY2FuIGtlZXAgdGhlIHRpbWVyCj4gYXJtZWQsIGJ1dCBub3QgcmUt YXJtIGl0IGFmdGVyIHRoZSBleHBpcmF0aW9uIGlmIHRoZSBDUFUgaXMgaWRsZS4KClNvIG11Y2gg Zm9yIHRoZSB0aGVvcnkuIFRoZSBOT0haIGxvZ2ljIGhhcyB0byByZXByb2dyYW0gdGhlIHRpbWVy IHdoZW4gdGhlCm5leHQgZXhwaXJ5IGlzIGZhcnRoZXIgYXdheSB0aGFuIHRoZSBuZXh0IHRpY2su IE90aGVyd2lzZSB5b3Ugd2FrZSB1cCBvbgpldmVyeSBpZGxlIGVudHJ5IG9uY2UgZm9yIG5vdGhp bmcsIHdoaWNoIGRlZmVhdHMgdGhlIHdob2xlIHB1cnBvc2Ugb2YgTk9IWgp0byBub3QgZG8gdGhh dC4KClRoYW5rcywKCgl0Z2x4Cg== From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll Date: Tue, 4 Jul 2017 16:50:54 +0200 (CEST) Message-ID: References: <4444ffc8-9e7b-5bd2-20da-af422fe834cc@redhat.com> <2245bef7-b668-9265-f3f8-3b63d71b1033@gmail.com> <7d085956-2573-212f-44f4-86104beba9bb@gmail.com> <05ec7efc-fb9c-ae24-5770-66fc472545a4@redhat.com> <20170627134043.GA1487@potion> <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com> <20170627142251.GB1487@potion> <20170704141322.GC30880@potion> Mime-Version: 1.0 Content-Type: multipart/mixed; BOUNDARY="8323329-169293439-1499179855=:9000" Cc: Yang Zhang , Paolo Bonzini , Wanpeng Li , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Jonathan Corbet , tony.luck@intel.com, Borislav Petkov , Peter Zijlstra , mchehab@kernel.org, Andrew Morton , krzk@kernel.org, jpoimboe@redhat.com, Andy Lutomirski , Christian Borntraeger , Thomas Garnier , Robert Gerst , Mathias Krause , douly.fnst@cn.fujitsu.com, Nicolai Stange , Frederic Weisbecker , dvlasenk@redhat.com, To: =?ISO-8859-2?Q?Radim_Kr=E8m=E1=F8?= Return-path: In-Reply-To: <20170704141322.GC30880@potion> Sender: linux-doc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-169293439-1499179855=:9000 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: 8BIT On Tue, 4 Jul 2017, Radim Krèmáø wrote: > I think there is a nicer solution to avoid the expensive timer rewrite: > Linux uses one-shot APIC timers and getting the timer interrupt is about > as expensive as programming the timer, so the guest can keep the timer > armed, but not re-arm it after the expiration if the CPU is idle. So much for the theory. The NOHZ logic has to reprogram the timer when the next expiry is farther away than the next tick. Otherwise you wake up on every idle entry once for nothing, which defeats the whole purpose of NOHZ to not do that. Thanks, tglx --8323329-169293439-1499179855=:9000--