From: Roman Kagan <rkagan@virtuozzo.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Sasha Levin <sashal@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Michael Kelley <mikelley@microsoft.com>,
Joe Perches <joe@perches.com>
Subject: Re: [PATCH v2] x86/hyper-v: micro-optimize send_ipi_one case
Date: Fri, 25 Oct 2019 14:05:34 +0000 [thread overview]
Message-ID: <20191025140528.GB23240@rkaganb.sw.ru> (raw)
In-Reply-To: <20191025131546.18794-1-vkuznets@redhat.com>
On Fri, Oct 25, 2019 at 03:15:46PM +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)).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> Changes since v1:
> - Style changes [Roman, Joe]
> ---
> arch/x86/hyperv/hv_apic.c | 13 ++++++++++---
> arch/x86/include/asm/trace/hyperv.h | 15 +++++++++++++++
> 2 files changed, 25 insertions(+), 3 deletions(-)
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
next prev parent reply other threads:[~2019-10-25 14:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-25 13:15 [PATCH v2] x86/hyper-v: micro-optimize send_ipi_one case Vitaly Kuznetsov
2019-10-25 14:05 ` Roman Kagan [this message]
2019-10-25 17:16 ` Michael Kelley
2019-10-25 17:26 ` Vitaly Kuznetsov
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