linux-kernel - Re: [PATCH] x86/hyper-v: enable TSC page clocksource on 32bit

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Message-ID: <alpine.DEB.2.21.1908212321320.1983@nanos.tec.linutronix.de>
Date:   Wed, 21 Aug 2019 23:23:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/hyper-v: enable TSC page clocksource on 32bit

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@...hat.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.

Thanks,

	tglx