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From: Thomas Gleixner <tglx@linutronix.de>
To: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Richard Cochran <richardcochran@gmail.com>,
	netdev@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	"Christopher S . Hall" <christopher.s.hall@intel.com>
Subject: Re: [RFC PATCH 1/5] x86: tsc: add tsc to art helpers
Date: Tue, 16 Jul 2019 09:57:35 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1907160952040.1767@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20190716072038.8408-2-felipe.balbi@linux.intel.com>

Felipe,

On Tue, 16 Jul 2019, Felipe Balbi wrote:

-ENOCHANGELOG

As you said in the cover letter:

>  (3) The change in arch/x86/kernel/tsc.c needs to be reviewed at length
>      before going in.

So some information what those interfaces are used for and why they are
needed would be really helpful.

> +void get_tsc_ns(struct system_counterval_t *tsc_counterval, u64 *tsc_ns)
> +{
> +	u64 tmp, res, rem;
> +	u64 cycles;
> +
> +	tsc_counterval->cycles = clocksource_tsc.read(NULL);
> +	cycles = tsc_counterval->cycles;
> +	tsc_counterval->cs = art_related_clocksource;
> +
> +	rem = do_div(cycles, tsc_khz);
> +
> +	res = cycles * USEC_PER_SEC;
> +	tmp = rem * USEC_PER_SEC;
> +
> +	do_div(tmp, tsc_khz);
> +	res += tmp;
> +
> +	*tsc_ns = res;
> +}
> +EXPORT_SYMBOL(get_tsc_ns);
> +
> +u64 get_art_ns_now(void)
> +{
> +	struct system_counterval_t tsc_cycles;
> +	u64 tsc_ns;
> +
> +	get_tsc_ns(&tsc_cycles, &tsc_ns);
> +
> +	return tsc_ns;
> +}
> +EXPORT_SYMBOL(get_art_ns_now);

While the changes look innocuous I'm missing the big picture why this needs
to emulate ART instead of simply using TSC directly.

Thanks,

	tglx

  reply	other threads:[~2019-07-16  7:57 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-16  7:20 [RFC PATCH 0/5] PTP: add support for Intel's TGPIO controller Felipe Balbi
2019-07-16  7:20 ` [RFC PATCH 1/5] x86: tsc: add tsc to art helpers Felipe Balbi
2019-07-16  7:57   ` Thomas Gleixner [this message]
2019-08-15  5:57     ` Felipe Balbi
2019-08-15 14:16       ` Thomas Gleixner
2019-10-01 10:24         ` Felipe Balbi
2019-10-17 11:15           ` Thomas Gleixner
2019-10-17 12:01             ` Felipe Balbi
2019-07-16  7:20 ` [RFC PATCH 2/5] PTP: add a callback for counting timestamp events Felipe Balbi
2019-07-16  7:20 ` [RFC PATCH 3/5] PTP: implement PTP_EVENT_COUNT_TSTAMP ioctl Felipe Balbi
2019-07-16  7:20 ` [RFC PATCH 4/5] PTP: Add flag for non-periodic output Felipe Balbi
2019-07-16 16:39   ` Richard Cochran
2019-07-17  6:49     ` Felipe Balbi
2019-07-17 17:36       ` Richard Cochran
2019-07-18  8:59         ` Felipe Balbi
2019-07-18 16:41           ` Richard Cochran
2019-08-13  7:53             ` Felipe Balbi
2019-08-13 17:48               ` Richard Cochran
2019-08-13 18:06                 ` Richard Cochran
2019-08-14  7:05                   ` Felipe Balbi
2019-07-16  7:20 ` [RFC PATCH 5/5] PTP: Add support for Intel PMC Timed GPIO Controller Felipe Balbi
2019-07-16 19:14   ` Shannon Nelson
2019-07-17  6:51     ` Felipe Balbi
2019-07-16 16:41 ` [RFC PATCH 0/5] PTP: add support for Intel's TGPIO controller Richard Cochran
2019-07-17  6:52   ` Felipe Balbi
2019-07-17 17:39     ` Richard Cochran
2019-07-18  8:58       ` Felipe Balbi
2019-07-18 19:50 ` Andrew Lunn
2019-07-19  7:35   ` Felipe Balbi
2019-07-19 13:20     ` Andrew Lunn
2019-08-13  7:50       ` Felipe Balbi
2019-08-13 17:49         ` Richard Cochran

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