linux-kernel - Re: [PATCH v2 13/17] x86/tsc: Rename native_read_tsc() to rdtsc

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Message-ID: <20150613085758.GB3796@pd.tnic>
Date:	Sat, 13 Jun 2015 10:57:59 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Huang Rui <ray.huang@....com>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH v2 13/17] x86/tsc: Rename native_read_tsc() to
 rdtsc_unordered()

On Fri, Jun 12, 2015 at 04:44:53PM -0700, Andy Lutomirski wrote:
> Now that there is no paravirt TSC, the "native" is inappropriate.
> The fact that rdtsc is not ordered can catch people by surprise, so
> call it rdtsc_unordered().
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

...

> @@ -109,7 +109,16 @@ notrace static inline int native_write_msr_safe(unsigned int msr,
>  extern int rdmsr_safe_regs(u32 regs[8]);
>  extern int wrmsr_safe_regs(u32 regs[8]);
>  
> -static __always_inline unsigned long long native_read_tsc(void)
> +/**
> + * rdtsc_unordered() - returns the current TSC without ordering constraints
> + *
> + * rdtsc_unordered() returns the result of RDTSC as a 64-bit integer.  The
> + * only ordering constraint it supplies is the ordering implied by
> + * "asm volatile": it will put the RDTSC in the place you expect.  The
> + * CPU can and will speculatively execute that RDTSC, though, so the
> + * results can be non-monotonic if compared on different CPUs.
> + */
> +static __always_inline unsigned long long rdtsc_unordered(void)

I like the rdtsc_ordered() thing because it wraps the barrier and people
cannot just forget it. But let's call this not rdtsc_unordered() but
simply

	rdtsc()

The "_unordered" suffix is unnecessary IMO since this function is a
simple wrapper around the hw insn and we do that naming scheme with all
such wrappers.

-- 
Regards/Gruss,
    Boris.

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