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Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Sasha Levin , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Michael Kelley Subject: Re: [PATCH] x86/hyper-v: micro-optimize send_ipi_one case Thread-Topic: [PATCH] x86/hyper-v: micro-optimize send_ipi_one case Thread-Index: AQHVioF8f6JnvYZ8LUKUUp53PHF9w6dp/CAA Date: Thu, 24 Oct 2019 16:32:07 +0000 Message-ID: <20191024163204.GA4673@rkaganb.sw.ru> References: <20191024152152.25577-1-vkuznets@redhat.com> In-Reply-To: <20191024152152.25577-1-vkuznets@redhat.com> Accept-Language: en-US, ru-RU Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mutt/1.12.1 (2019-06-15) mail-followup-to: Roman Kagan , Vitaly Kuznetsov , linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Sasha Levin , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Michael Kelley x-originating-ip: [185.231.240.5] x-clientproxiedby: HE1P18901CA0020.EURP189.PROD.OUTLOOK.COM (2603:10a6:3:8b::30) To AM4PR0802MB2242.eurprd08.prod.outlook.com (2603:10a6:200:5f::15) authentication-results: spf=none (sender IP is ) smtp.mailfrom=rkagan@virtuozzo.com; x-ms-exchange-messagesentrepresentingtype: 1 x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 3a944c21-b0e2-48f0-7f95-08d7589fb5ff x-ms-traffictypediagnostic: AM4PR0802MB2305:|AM4PR0802MB2305:|AM4PR0802MB2305: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:7691; x-forefront-prvs: 0200DDA8BE x-forefront-antispam-report: SFV:SPM;SFS:(10019020)(39840400004)(366004)(376002)(136003)(346002)(396003)(189003)(199004)(229853002)(6486002)(9686003)(305945005)(2906002)(7736002)(76176011)(52116002)(4326008)(6246003)(33656002)(6512007)(1076003)(316002)(6436002)(256004)(14454004)(86362001)(186003)(66556008)(64756008)(66446008)(26005)(81156014)(8676002)(81166006)(8936002)(99286004)(66476007)(478600001)(66946007)(5660300002)(66066001)(54906003)(446003)(6116002)(36756003)(25786009)(58126008)(386003)(6506007)(11346002)(7416002)(6916009)(102836004)(486006)(476003)(71190400001)(71200400001)(3846002)(14444005)(30126002);DIR:OUT;SFP:1501;SCL:5;SRVR:AM4PR0802MB2305;H:AM4PR0802MB2242.eurprd08.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A:1; received-spf: None (protection.outlook.com: virtuozzo.com does not designate permitted sender hosts) x-ms-exchange-transport-forked: True x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 Content-Type: text/plain; charset="us-ascii" Content-ID: <03073080DC5DAE4AA941C4E9409541E0@eurprd08.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3a944c21-b0e2-48f0-7f95-08d7589fb5ff X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Oct 2019 16:32:07.5388 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: VRg6FX4h/YS9Af2t+BBdUbfhinXHpy+bvFI9uZxOxiO2VrtezmuIgJzZiWEMiYXLsPG6V4uVUTtF3df9TX4X5w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM4PR0802MB2305 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 24, 2019 at 05:21:52PM +0200, Vitaly Kuznetsov wrote: > When sending an IPI to a single CPU there is no need to deal with cpumasks. > With 2 CPU guest on WS2019 I'm seeing a minor (like 3%, 8043 -> 7761 CPU > cycles) improvement with smp_call_function_single() loop benchmark. The > optimization, however, is tiny and straitforward. Also, send_ipi_one() is > important for PV spinlock kick. > > I was also wondering if it would make sense to switch to using regular > APIC IPI send for CPU > 64 case but no, it is twice as expesive (12650 CPU > cycles for __send_ipi_mask_ex() call, 26000 for orig_apic.send_IPI(cpu, > vector)). Is it with APICv or emulated apic? > Signed-off-by: Vitaly Kuznetsov > --- > arch/x86/hyperv/hv_apic.c | 22 +++++++++++++++++++--- > arch/x86/include/asm/trace/hyperv.h | 15 +++++++++++++++ > 2 files changed, 34 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c > index e01078e93dd3..847f9d0328fe 100644 > --- a/arch/x86/hyperv/hv_apic.c > +++ b/arch/x86/hyperv/hv_apic.c > @@ -194,10 +194,26 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector) > > static bool __send_ipi_one(int cpu, int vector) > { > - struct cpumask mask = CPU_MASK_NONE; > + int ret; > > - cpumask_set_cpu(cpu, &mask); > - return __send_ipi_mask(&mask, vector); > + trace_hyperv_send_ipi_one(cpu, vector); > + > + if (unlikely(!hv_hypercall_pg)) > + return false; > + > + if (unlikely((vector < HV_IPI_LOW_VECTOR) || > + (vector > HV_IPI_HIGH_VECTOR))) > + return false; I guess 'ulikely' is unnecessary in these cases. > + > + if (cpu >= 64) > + goto do_ex_hypercall; > + > + ret = hv_do_fast_hypercall16(HVCALL_SEND_IPI, vector, > + BIT_ULL(hv_cpu_number_to_vp_number(cpu))); > + return ((ret == 0) ? true : false); D'oh. Isn't "return ret == 0;" or just "return ret;" good enough? These tiny nitpicks are no reason to hold the patch though, so Reviewed-by: Roman Kagan