Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Nadav Amit <namit@vmware.com>
To:     Thomas Gleixner <tglx@linutronix.de>
CC:     LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Feng Tang <feng.tang@intel.com>
Subject: Re: [patch V2 21/25] x86/smp: Enhance native_send_call_func_ipi()
Thread-Topic: [patch V2 21/25] x86/smp: Enhance native_send_call_func_ipi()
Thread-Index: AQHVMoZQ1wtoUEJrLk6xt836w3tppqa7PDEA
Date:   Fri, 5 Jul 2019 01:26:10 +0000
Message-ID: <C77F4C58-9CA3-4784-AE98-A9D6EDD4A788@vmware.com>
References: <20190704155145.617706117@linutronix.de>
 <20190704155610.325211809@linutronix.de>
In-Reply-To: <20190704155610.325211809@linutronix.de>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: vmware.com does not designate
 permitted sender hosts)
Content-Type: text/plain; charset="us-ascii"
Content-ID: <E9DC42EBEF48FC4794CF1D7AB2C3AEEB@namprd05.prod.outlook.com>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: e246ec79-79f4-410c-b700-08d700e7c2f2
X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Jul 2019 01:26:10.2257
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: b39138ca-3cee-4b4a-a4d6-cd83d9dd62f0
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: namit@vmware.com
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR05MB5864
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> On Jul 4, 2019, at 8:52 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
>=20
> Nadav noticed that the cpumask allocations in native_send_call_func_ipi()
> are noticeable in microbenchmarks.
>=20
> Use the new cpumask_or_equal() function to simplify the decision whether
> the supplied target CPU mask is either equal to cpu_online_mask or equal =
to
> cpu_online_mask except for the CPU on which the function is invoked.
>=20
> cpumask_or_equal() or's the target mask and the cpumask of the current CP=
U
> together and compares it to cpu_online_mask.
>=20
> If the result is false, use the mask based IPI function, otherwise check
> whether the current CPU is set in the target mask and invoke either the
> send_IPI_all() or the send_IPI_allbutselt() APIC callback.
>=20
> Make the shorthand decision also depend on the static key which enables
> shorthand mode. That allows to remove the extra cpumask comparison with
> cpu_callout_mask.
>=20
> Reported-by: Nadav Amit <namit@vmware.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> V2: New patch
> ---
> arch/x86/kernel/apic/ipi.c |   24 +++++++++++-------------
> 1 file changed, 11 insertions(+), 13 deletions(-)
>=20
> --- a/arch/x86/kernel/apic/ipi.c
> +++ b/arch/x86/kernel/apic/ipi.c
> @@ -83,23 +83,21 @@ void native_send_call_func_single_ipi(in
>=20
> void native_send_call_func_ipi(const struct cpumask *mask)
> {
> -	cpumask_var_t allbutself;
> +	if (static_branch_likely(&apic_use_ipi_shorthand)) {
> +		unsigned int cpu =3D smp_processor_id();
>=20
> -	if (!alloc_cpumask_var(&allbutself, GFP_ATOMIC)) {
> -		apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
> +		if (!cpumask_or_equal(mask, cpumask_of(cpu), cpu_online_mask))
> +			goto sendmask;
> +
> +		if (cpumask_test_cpu(cpu, mask))
> +			apic->send_IPI_all(CALL_FUNCTION_VECTOR);
> +		else if (num_online_cpus() > 1)
> +			apic->send_IPI_allbutself(CALL_FUNCTION_VECTOR);
> 		return;
> 	}
>=20
> -	cpumask_copy(allbutself, cpu_online_mask);
> -	cpumask_clear_cpu(smp_processor_id(), allbutself);
> -
> -	if (cpumask_equal(mask, allbutself) &&
> -	    cpumask_equal(cpu_online_mask, cpu_callout_mask))
> -		apic->send_IPI_allbutself(CALL_FUNCTION_VECTOR);
> -	else
> -		apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
> -
> -	free_cpumask_var(allbutself);
> +sendmask:
> +	apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
> }
>=20
> #endif /* CONFIG_SMP */

It does look better and simpler than my solution.