From: Thomas Gleixner <tglx@linutronix.de>
To: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org,
Daniel Lezcano <daniel.lezcano@linaro.org>,
devicetree@vger.kernel.org,
Andrew Bresticker <abrestic@chromium.org>,
James Hartley <james.hartley@imgtec.com>,
James Hogan <james.hogan@imgtec.com>,
Damien.Horsley@imgtec.com, Govindraj.Raja@imgtec.com
Subject: Re: [PATCH 6/7] clocksource: Add Pistachio clocksource-only driver
Date: Fri, 22 May 2015 00:09:42 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1505220009120.5457@nanos> (raw)
In-Reply-To: <555E55F4.2060500@imgtec.com>
On Thu, 21 May 2015, Ezequiel Garcia wrote:
> On 05/21/2015 07:00 PM, Thomas Gleixner wrote:
> > On Thu, 21 May 2015, Ezequiel Garcia wrote:
> >> +static cycle_t clocksource_read_cycles(struct clocksource *cs)
> >> +{
> >> + u32 counter, overflw;
> >> + unsigned long flags;
> >> +
> >> + raw_spin_lock_irqsave(&lock, flags);
> >
> > Hmm. Is that lock really necessary to read that counter? The
> > clocksource is global. And if its actually used for timekeeping, the
> > lock can get heavy contended.
> >
>
> Yup, it is really (and sadly) necessary. The kernel hangs up completely
> without it when the counter is accesed by more than one CPU.
>
> Apparently, those two timer registers overflow and counter must be read
> atomically.
Welcome to the wonderful world of useless timer hardware.
tglx
next prev parent reply other threads:[~2015-05-21 22:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-21 21:37 [PATCH 0/7] Clocksource changes for Pistachio CPUFreq Ezequiel Garcia
2015-05-21 21:37 ` [PATCH 1/7] clocksource: mips-gic: Enable the clock before using it Ezequiel Garcia
2015-05-21 22:17 ` Andrew Bresticker
2015-05-21 21:37 ` [PATCH 2/7] clocksource: mips-gic: Add missing error returns checks Ezequiel Garcia
2015-05-21 22:18 ` Andrew Bresticker
2015-05-21 21:37 ` [PATCH 3/7] clocksource: mips-gic: Split clocksource and clockevent initialization Ezequiel Garcia
2015-05-21 22:24 ` Andrew Bresticker
2015-05-21 22:25 ` Ezequiel Garcia
2015-05-22 16:53 ` Andrew Bresticker
2015-05-21 21:37 ` [PATCH 4/7] clocksource: mips-gic: Update clockevent frequency on clock rate changes Ezequiel Garcia
2015-05-21 22:32 ` Andrew Bresticker
2015-05-21 22:30 ` Ezequiel Garcia
2015-05-21 21:41 ` [PATCH 5/7] clocksource: Add Pistachio SoC general purpose timer binding document Ezequiel Garcia
2015-05-21 23:41 ` Andrew Bresticker
2015-05-21 21:41 ` [PATCH 6/7] clocksource: Add Pistachio clocksource-only driver Ezequiel Garcia
2015-05-21 22:00 ` Thomas Gleixner
2015-05-21 22:02 ` Ezequiel Garcia
2015-05-21 22:09 ` Thomas Gleixner [this message]
2015-05-22 16:48 ` Andrew Bresticker
2015-05-26 14:16 ` Ezequiel Garcia
2015-05-21 21:43 ` [PATCH 7/7] mips: pistachio: Allow to enable the external timer based clocksource Ezequiel Garcia
2015-05-22 16:50 ` Andrew Bresticker
2015-05-22 16:58 ` James Hartley
2015-05-22 18:08 ` Ezequiel Garcia
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