linux-kernel - Re: [PATCH] x86/hpet: Reduce HPET counter read contention

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Message-ID: <CALCETrWzS0MGTtDLecuwZa4ikvGAYHwWf-4gDjti=DV6gb1V+g@mail.gmail.com>
Date:	Thu, 7 Apr 2016 17:13:40 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Waiman Long <waiman.long@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Jiang Liu <jiang.liu@...ux.intel.com>,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Randy Wright <rwright@....com>
Subject: Re: [PATCH] x86/hpet: Reduce HPET counter read contention

On Thu, Apr 7, 2016 at 8:07 AM, Waiman Long <waiman.long@....com> wrote:
> On 04/07/2016 12:58 AM, Andy Lutomirski wrote:
>> Reading the HPET is so slow that all the atomic ops in the world won't
>> make a dent.  Why not just turn this optimization on unconditionally?
>>
>> --Andy
>
>
> I am constantly on the alert that we should not introduce regression on
> lesser systems like a single socket machine with a few cores. That is why I
> put the check to conditionally enable this optimization. I have no issue of
> taking that out and let it be the default as long as no one object.
>

Agreed.  I just suspect it's actually faster on all systems.

This reminds me -- I need to send out my patch to disable the vdso
HPET code, which will make your change more effective.  I'll cc you.

> Cheers,
> Longman



-- 
Andy Lutomirski
AMA Capital Management, LLC