linux-kernel - Re: [PATCH -v2] x86: Kill notsc

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Message-ID: <20151104102941.GA1235@pd.tnic>
Date:	Wed, 4 Nov 2015 11:29:41 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, x86-ml <x86@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2] x86: Kill notsc

On Wed, Nov 04, 2015 at 11:21:45AM +0100, Thomas Gleixner wrote:
> On Thu, 22 Oct 2015, Borislav Petkov wrote:
> >  u64 native_sched_clock(void)
> >  {
> > -	if (static_branch_likely(&__use_tsc)) {
> > -		u64 tsc_now = rdtsc();
> > -
> > -		/* return the value in ns */
> > -		return cycles_2_ns(tsc_now);
> > -	}
> > -
> > +#ifdef CONFIG_X86_TSC
> > +	/* return the value in ns */
> > +	return cycles_2_ns(rdtsc());
> > +#else
> >  	/*
> > -	 * Fall back to jiffies if there's no TSC available:
> > -	 * ( But note that we still use it if the TSC is marked
> > -	 *   unstable. We do this because unlike Time Of Day,
> > -	 *   the scheduler clock tolerates small errors and it's
> > -	 *   very important for it to be as fast as the platform
> > -	 *   can achieve it. )
> > +	 * Fall back to jiffies if there's no TSC available: ( But note that we
> > +	 * still use it if the TSC is marked unstable. We do this because unlike
> > +	 * Time Of Day, the scheduler clock tolerates small errors and it's very
> > +	 * important for it to be as fast as the platform can achieve it. )
> 
> This comment does not make any sense with this modification.

Ok.

My intention was to keep the aspect that we still can use the TSC here,
even if it is marked unstable. I'll move it over rdtsc().

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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