From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
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: Thu, 22 Aug 2019 09:52:14 +0200 [thread overview]
Message-ID: <877e75r61d.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1908212321320.1983@nanos.tec.linutronix.de>
Thomas Gleixner <tglx@linutronix.de> writes:
> On Wed, 21 Aug 2019, Thomas Gleixner wrote:
>
>> 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.
>
> That said, could you please rebase that on
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
>
> as I just applied the TSC page patches there and this conflicts left and
> right.
Sure, v2 is coming!
--
Vitaly
prev parent reply other threads:[~2019-08-22 7:52 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
2019-08-21 21:23 ` Thomas Gleixner
2019-08-22 7:52 ` Vitaly Kuznetsov [this message]
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