linux-kernel - Re: [PATCH] x86/tsc: mark tsc reliable for qualified platforms

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Date:   Tue, 2 Mar 2021 19:55:00 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, rui.zhang@...el.com,
        dave.hansen@...el.com, andi.kleen@...el.com, len.brown@...el.com
Subject: Re: [PATCH] x86/tsc: mark tsc reliable for qualified platforms

On Tue, Mar 02, 2021 at 10:14:01AM +0100, Peter Zijlstra wrote:
> On Tue, Mar 02, 2021 at 10:52:52AM +0800, Feng Tang wrote:
> > @@ -1193,6 +1193,17 @@ static void __init check_system_tsc_reliable(void)
> >  #endif
> >  	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
> >  		tsc_clocksource_reliable = 1;
> > +
> > +	/*
> > +	 * Ideally the socket number should be checked, but this is called
> > +	 * by tsc_init() which is in early boot phase and the socket numbers
> > +	 * may not be available. Use 'nr_online_nodes' as a fallback solution
> > +	 */
> > +	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC)
> > +		&& boot_cpu_has(X86_FEATURE_NONSTOP_TSC)
> > +		&& boot_cpu_has(X86_FEATURE_TSC_ADJUST)
> > +		&& nr_online_nodes <= 2)
> > +		tsc_clocksource_reliable = 1;
> 
> Logical operators go at the end of a line and alignment is with the (,
> not the code block after it.

Thanks for pointing out and the suggestion! Will change it to

	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
	    boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
	    boot_cpu_has(X86_FEATURE_TSC_ADJUST) &&
	    nr_online_nodes <= 2)
		tsc_clocksource_reliable = 1;

- Feng