From: Thomas Gleixner <tglx@linutronix.de>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Sasha Levin <sashal@kernel.org>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Michael Kelley <mikelley@microsoft.com>,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] x86/hyper-v: enable TSC page clocksource on 32bit
Date: Wed, 21 Aug 2019 23:17:35 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1908212316040.1983@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20190821095650.1841-1-vkuznets@redhat.com>
On Wed, 21 Aug 2019, Vitaly Kuznetsov wrote:
> There is no particular reason to not enable TSC page clocksource
> on 32-bit. mul_u64_u64_shr() is available and despite the increased
> computational complexity (compared to 64bit) TSC page is still a huge
> win compared to MSR-based clocksource.
>
> In-kernel reads:
> MSR based clocksource: 3361 cycles
> TSC page clocksource: 49 cycles
>
> Reads from userspace (unilizing vDSO in case of TSC page):
> MSR based clocksource: 5664 cycles
> TSC page clocksource: 131 cycles
>
> Enabling TSC page on 32bits allows us to get rid of CONFIG_HYPERV_TSCPAGE
s/allows us/allows/
> as it is now not any different from CONFIG_HYPERV_TIMER.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/include/asm/vdso/gettimeofday.h | 6 +++---
> drivers/clocksource/hyperv_timer.c | 11 -----------
> drivers/hv/Kconfig | 3 ---
> include/clocksource/hyperv_timer.h | 6 ++----
> 4 files changed, 5 insertions(+), 21 deletions(-)
Really nice cleanup as a side effect of adding functionality.
Thanks,
tglx
next prev parent reply other threads:[~2019-08-21 21:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 9:56 [PATCH] x86/hyper-v: enable TSC page clocksource on 32bit Vitaly Kuznetsov
2019-08-21 21:16 ` Michael Kelley
2019-08-21 21:17 ` Thomas Gleixner [this message]
2019-08-21 21:23 ` Thomas Gleixner
2019-08-22 7:52 ` Vitaly Kuznetsov
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