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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sasha Levin <sashal@kernel.org>
Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, "K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Roman Kagan <rkagan@virtuozzo.com>,
	Michael Kelley <mikelley@microsoft.com>,
	Joe Perches <joe@perches.com>
Subject: Re: [PATCH v3] x86/hyper-v: micro-optimize send_ipi_one case
Date: Thu, 07 Nov 2019 14:26:53 +0100
Message-ID: <877e4bbyw2.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20191027151938.7296-1-vkuznets@redhat.com>

Vitaly Kuznetsov <vkuznets@redhat.com> writes:

> 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)).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> Changes since v2:
>  - Check VP number instead of CPU number against >= 64 [Michael]
>  - Check for VP_INVAL

Hi Sasha,

do you have plans to pick this up for hyperv-next or should we ask x86
folks to?

Thanks!

-- 
Vitaly

  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-27 15:19 Vitaly Kuznetsov
2019-10-27 16:49 ` Michael Kelley
2019-10-28  9:35 ` Roman Kagan
2019-11-07 13:26 ` Vitaly Kuznetsov [this message]
2019-11-07 21:21   ` Thomas Gleixner

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