From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Zheng, Lv" Subject: RE: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader Date: Wed, 29 Apr 2015 00:49:59 +0000 Message-ID: <1AE640813FDE7649BE1B193DEA596E880270FB3B@SHSMSX101.ccr.corp.intel.com> References: <1427448178-20689-1-git-send-email-bp@alien8.de> <1427448178-20689-6-git-send-email-bp@alien8.de> <1AE640813FDE7649BE1B193DEA596E880270F835@SHSMSX101.ccr.corp.intel.com> <20150428135913.GD19025@pd.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from mga03.intel.com ([134.134.136.65]:40987 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031281AbbD2Aua (ORCPT ); Tue, 28 Apr 2015 20:50:30 -0400 Content-Language: en-US Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Borislav Petkov Cc: linux-edac , Jiri Kosina , Borislav Petkov , "Rafael J. Wysocki" , Len Brown , "Luck, Tony" , Tomasz Nowicki , "Chen, Gong" , Wolfram Sang , Naoya Horiguchi , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" SGksDQoNCj4gRnJvbTogWmhlbmcsIEx2DQo+IFNlbnQ6IFdlZG5lc2RheSwgQXByaWwgMjksIDIw MTUgODoyNSBBTQ0KPiBTdWJqZWN0OiBSRTogW1JGQyBQQVRDSCA1LzVdIEdIRVM6IE1ha2UgTk1J IGhhbmRsZXIgaGF2ZSBhIHNpbmdsZSByZWFkZXINCj4gDQo+IEhpLA0KPiANCj4gPiBGcm9tOiBC b3Jpc2xhdiBQZXRrb3YgW21haWx0bzpicEBhbGllbjguZGVdDQo+ID4gU2VudDogVHVlc2RheSwg QXByaWwgMjgsIDIwMTUgOTo1OSBQTQ0KPiA+IFN1YmplY3Q6IFJlOiBbUkZDIFBBVENIIDUvNV0g R0hFUzogTWFrZSBOTUkgaGFuZGxlciBoYXZlIGEgc2luZ2xlIHJlYWRlcg0KPiA+DQo+ID4gT24g VHVlLCBBcHIgMjgsIDIwMTUgYXQgMDE6Mzg6NDFQTSArMDAwMCwgWmhlbmcsIEx2IHdyb3RlOg0K PiA+ID4gPiAtCXJhd19zcGluX2xvY2soJmdoZXNfbm1pX2xvY2spOw0KPiA+ID4gPiArCWlmICgh YXRvbWljX2FkZF91bmxlc3MoJmdoZXNfaW5fbm1pLCAxLCAxKSkNCj4gPiA+ID4gKwkJcmV0dXJu IHJldDsNCj4gPiA+ID4gKw0KPiA+ID4NCj4gPiA+IGlmIChhdG9taWNfY21weGNoZygmZ2hlc19p bl9ubWksIDAsIDEpKQ0KPiA+ID4gCXJldHVybiByZXQ7DQo+ID4NCj4gPiBPaywgbm93IEkgdW5k ZXJzdGFuZCB3aGF0IHlvdSBtZWFuLg0KPiA+DQo+ID4gV2UgYWJzb2x1dGVseSB3YW50IHRvIHVz ZSBhdG9taWNfYWRkX3VubGVzcygpIGJlY2F1c2Ugd2UgZ2V0IHRvIHNhdmUgdXMNCj4gPiB0aGUg ZXhwZW5zaXZlDQo+ID4NCj4gPiAJTE9DSzsgQ01QWENIRw0KPiA+DQo+ID4gaWYgdGhlIHZhbHVl IHdhcyBhbHJlYWR5IDEuIFdoaWNoIGlzIGV4YWN0bHkgd2hhdCB0aGlzIHBhdGNoIGlzIHRyeWlu Zw0KPiA+IHRvIGF2b2lkIC0gYSB0aHVuZGVyaW5nIGhlcmQgb2YgY29yZXMgQ01QWENIR2luZyBh IGdsb2JhbCB2YXJpYWJsZS4NCj4gDQo+IElNTywgb24gbW9zdCBhcmNoaXRlY3R1cmVzLCB0aGUg ImNtcCIgcGFydCBzaG91bGQgd29yayBqdXN0IGxpa2Ugd2hhdCB5b3UndmUgZG9uZSB3aXRoICJp ZiIuDQo+IEFuZCBvbiBzb21lIGFyY2hpdGVjdHVyZXMsIGlmIHRoZSAieGNoZyIgZG9lc24ndCBo YXBwZW4sIHRoZSAiY21wIiBwYXJ0IGV2ZW4gd29uJ3QgY2F1c2UgYSBwaXBlIGxpbmUgaGF6YXJk Lg0KDQpJZiB5b3UgbWFuIHRoZSBMT0NLIHByZWZpeCwgSSB1bmRlcnN0YW5kIG5vdy4NCg0KVGhh bmtzIGFuZCBiZXN0IHJlZ2FyZHMNCi1Mdg0KDQo+IA0KPiBUaGFua3MgYW5kIGJlc3QgcmVnYXJk cw0KPiAtTHYNCj4gDQo+IA0KPiA+DQo+ID4gSS5lLiwNCj4gPg0KPiA+IAltb3ZsCWdoZXNfaW5f bm1pKCVyaXApLCAlZWN4CSMgTUVNWyhjb25zdCBpbnQgKikmZ2hlc19pbl9ubWldLCBjDQo+ID4g CWNtcGwJJDEsICVlY3gJIywgYw0KPiA+IAlqZQkuTDMxMQkjLAkJCQk8LS0tIGV4aXQgaGVyZSBp ZiBnaGVzX2luX25taSA9PSAxLg0KPiA+IAlsZWFsCTEoJXJjeCksICVlZHgJIywgRC4zNzE2Mw0K PiA+IAltb3ZsCSVlY3gsICVlYXgJIyBjLCBjDQo+ID4gI0FQUA0KPiA+ICMgMTc3ICIuL2FyY2gv eDg2L2luY2x1ZGUvYXNtL2F0b21pYy5oIiAxDQo+ID4gCS5wdXNoc2VjdGlvbiAuc21wX2xvY2tz LCJhIg0KPiA+IC5iYWxpZ24gNA0KPiA+IC5sb25nIDY3MWYgLSAuDQo+ID4gLnBvcHNlY3Rpb24N Cj4gPiA2NzE6DQo+ID4gCWxvY2s7IGNtcHhjaGdsICVlZHgsZ2hlc19pbl9ubWkoJXJpcCkJIyBE LjM3MTYzLCBNRU1bKHZvbGF0aWxlIHUzMiAqKSZnaGVzX2luX25taV0NCj4gPiAjIDAgIiIgMg0K PiA+ICNOT19BUFANCj4gPg0KPiA+IC0tDQo+ID4gUmVnYXJkcy9HcnVzcywNCj4gPiAgICAgQm9y aXMuDQo+ID4NCj4gPiBFQ08gdGlwICMxMDE6IFRyaW0geW91ciBtYWlscyB3aGVuIHlvdSByZXBs eS4NCj4gPiAtLQ0K From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031418AbbD2Aue (ORCPT ); Tue, 28 Apr 2015 20:50:34 -0400 Received: from mga03.intel.com ([134.134.136.65]:40987 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031281AbbD2Aua (ORCPT ); Tue, 28 Apr 2015 20:50:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,667,1422950400"; d="scan'208";a="687169411" From: "Zheng, Lv" To: Borislav Petkov CC: linux-edac , Jiri Kosina , Borislav Petkov , "Rafael J. Wysocki" , "Len Brown" , "Luck, Tony" , Tomasz Nowicki , "Chen, Gong" , Wolfram Sang , Naoya Horiguchi , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader Thread-Topic: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader Thread-Index: AQHQaG/ro4UZP9zjdEyK4aA7ppX1rp1imlXQ//+FsoCAATPzQIAAB3pA Date: Wed, 29 Apr 2015 00:49:59 +0000 Message-ID: <1AE640813FDE7649BE1B193DEA596E880270FB3B@SHSMSX101.ccr.corp.intel.com> References: <1427448178-20689-1-git-send-email-bp@alien8.de> <1427448178-20689-6-git-send-email-bp@alien8.de> <1AE640813FDE7649BE1B193DEA596E880270F835@SHSMSX101.ccr.corp.intel.com> <20150428135913.GD19025@pd.tnic> Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id t3T0oabl023021 Hi, > From: Zheng, Lv > Sent: Wednesday, April 29, 2015 8:25 AM > Subject: RE: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader > > Hi, > > > From: Borislav Petkov [mailto:bp@alien8.de] > > Sent: Tuesday, April 28, 2015 9:59 PM > > Subject: Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader > > > > On Tue, Apr 28, 2015 at 01:38:41PM +0000, Zheng, Lv wrote: > > > > - raw_spin_lock(&ghes_nmi_lock); > > > > + if (!atomic_add_unless(&ghes_in_nmi, 1, 1)) > > > > + return ret; > > > > + > > > > > > if (atomic_cmpxchg(&ghes_in_nmi, 0, 1)) > > > return ret; > > > > Ok, now I understand what you mean. > > > > We absolutely want to use atomic_add_unless() because we get to save us > > the expensive > > > > LOCK; CMPXCHG > > > > if the value was already 1. Which is exactly what this patch is trying > > to avoid - a thundering herd of cores CMPXCHGing a global variable. > > IMO, on most architectures, the "cmp" part should work just like what you've done with "if". > And on some architectures, if the "xchg" doesn't happen, the "cmp" part even won't cause a pipe line hazard. If you man the LOCK prefix, I understand now. Thanks and best regards -Lv > > Thanks and best regards > -Lv > > > > > > I.e., > > > > movl ghes_in_nmi(%rip), %ecx # MEM[(const int *)&ghes_in_nmi], c > > cmpl $1, %ecx #, c > > je .L311 #, <--- exit here if ghes_in_nmi == 1. > > leal 1(%rcx), %edx #, D.37163 > > movl %ecx, %eax # c, c > > #APP > > # 177 "./arch/x86/include/asm/atomic.h" 1 > > .pushsection .smp_locks,"a" > > .balign 4 > > .long 671f - . > > .popsection > > 671: > > lock; cmpxchgl %edx,ghes_in_nmi(%rip) # D.37163, MEM[(volatile u32 *)&ghes_in_nmi] > > # 0 "" 2 > > #NO_APP > > > > -- > > Regards/Gruss, > > Boris. > > > > ECO tip #101: Trim your mails when you reply. > > -- {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I