From: Matthieu CASTET <matthieu.castet@parrot.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Simon Glass <sjg@chromium.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 0/3] Add accurate boot timing to a Linux system
Date: Mon, 26 Sep 2011 09:53:33 +0200 [thread overview]
Message-ID: <4E802F7D.9000006@parrot.com> (raw)
In-Reply-To: <20110924083203.GZ17169@n2100.arm.linux.org.uk>
Hi,
Russell King - ARM Linux a écrit :
> On Fri, Sep 23, 2011 at 04:03:15PM -0700, Simon Glass wrote:
>> An accurate timer is required to make the numbers meaningful. Many
>> modern platforms have a microsecond timer. This patch set uses a
>> function called timer_get_us() to read the timer.
>
> Not another 'get a time value' function. Why do we need soo many?
> We have - at least:
>
> ktime_get (and various flavours of it)
> do_gettimeofday
> getnstimeofday
> sched_clock
>
> Do we really need yet another one which will have to be multiplexed
> amongst platforms, requiring scaling and so forth from whatever the
> platform provides?
>
> Remember that ARM timers are virtually all MMIO mapped, which means
> they don't work during early kernel bringup when the MMU mappings for
> the hardware have not been setup. (That's the reason stuff like
> sched_clock for printk doesn't work early.)
Doesn't cortexA-8 (and A9 ?) have a cycle counter that can be read by
coprocessor 15 ?
Couldn't we use that counter for early stuff on those architectures ?
Matthieu
next prev parent reply other threads:[~2011-09-26 7:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-23 23:03 [RFC PATCH 0/3] Add accurate boot timing to a Linux system Simon Glass
2011-09-23 23:03 ` [RFC PATCH 1/3] bootstage: Add bootstages to record timing in the kernel Simon Glass
2011-09-23 23:03 ` [RFC PATCH 2/3] bootstage: Insert bootstage_mark to record timing for bootup Simon Glass
2011-09-25 12:59 ` Bjorn Helgaas
2011-09-23 23:03 ` [RFC PATCH 3/3] bootstage: Get u-boot timing from the device tree Simon Glass
2011-09-23 23:34 ` [RFC PATCH 0/3] Add accurate boot timing to a Linux system Valdis.Kletnieks
2011-09-24 4:10 ` Simon Glass
2011-09-24 8:32 ` Russell King - ARM Linux
2011-09-24 14:06 ` Simon Glass
2011-09-26 7:53 ` Matthieu CASTET [this message]
2011-09-27 18:29 ` Simon Glass
2011-09-25 12:54 ` Bjorn Helgaas
2011-09-27 18:26 ` Simon Glass
2011-09-27 17:56 ` Tim Bird
2011-09-27 17:57 ` Tim Bird
2011-09-27 18:42 ` Simon Glass
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