From: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
To: Ezequiel Garcia
<ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-mips-6z/3iImG2C8G8FEW9MqTrA@public.gmane.org,
Daniel Lezcano
<daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Andrew Bresticker
<abrestic-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
James Hartley
<james.hartley-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>,
James Hogan <james.hogan-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>,
Damien.Horsley-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org,
Govindraj.Raja-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org
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: <555E55F4.2060500-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
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
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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 2/7] clocksource: mips-gic: Add missing error returns checks Ezequiel Garcia
[not found] ` <1432244260-14908-3-git-send-email-ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2015-05-21 22:18 ` Andrew Bresticker
[not found] ` <1432244260-14908-1-git-send-email-ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2015-05-21 21:37 ` [PATCH 1/7] clocksource: mips-gic: Enable the clock before using it Ezequiel Garcia
[not found] ` <1432244260-14908-2-git-send-email-ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2015-05-21 22:17 ` 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
[not found] ` <CAL1qeaFkzpH+nGqRPOuY-L62jP8NgZWP0WxKTYKXZDpe1sSojg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-05-21 22:25 ` Ezequiel Garcia
[not found] ` <555E5B5C.9050807-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
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
[not found] ` <1432244260-14908-5-git-send-email-ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2015-05-21 22:32 ` Andrew Bresticker
[not found] ` <CAL1qeaEzKh6H8HBCULJWM4yMnSQGexWmV0rrnYMViMpuzKWyLg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-05-21 22:30 ` Ezequiel Garcia
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
[not found] ` <555E55F4.2060500-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2015-05-21 22:09 ` Thomas Gleixner [this message]
2015-05-22 16:48 ` Andrew Bresticker
[not found] ` <CAL1qeaEL7D6=WpyigbHWv8DEhp0XhC4acCYRkQ6Fm0Wr4HW11A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-05-26 14:16 ` 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 21:43 ` [PATCH 7/7] mips: pistachio: Allow to enable the external timer based clocksource Ezequiel Garcia
[not found] ` <1432244618-15548-1-git-send-email-ezequiel.garcia-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
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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