From: matthieu.castet@parrot.com (Matthieu CASTET)
To: linux-arm-kernel@lists.infradead.org
Subject: [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 ?crit :
> 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
WARNING: multiple messages have this Message-ID (diff)
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: 32+ 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 ` 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 ` Simon Glass
2011-09-23 23:03 ` [RFC PATCH 2/3] bootstage: Insert bootstage_mark to record timing for bootup Simon Glass
2011-09-23 23:03 ` Simon Glass
2011-09-25 12:59 ` Bjorn Helgaas
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 23:03 ` Simon Glass
2011-09-23 23:34 ` [RFC PATCH 0/3] Add accurate boot timing to a Linux system Valdis.Kletnieks at vt.edu
2011-09-23 23:34 ` Valdis.Kletnieks
2011-09-24 4:10 ` Simon Glass
2011-09-24 4:10 ` Simon Glass
2011-09-24 8:32 ` Russell King - ARM Linux
2011-09-24 8:32 ` Russell King - ARM Linux
2011-09-24 14:06 ` Simon Glass
2011-09-24 14:06 ` Simon Glass
2011-09-26 7:53 ` Matthieu CASTET [this message]
2011-09-26 7:53 ` Matthieu CASTET
2011-09-27 18:29 ` Simon Glass
2011-09-27 18:29 ` Simon Glass
2011-09-25 12:54 ` Bjorn Helgaas
2011-09-25 12:54 ` Bjorn Helgaas
2011-09-27 18:26 ` Simon Glass
2011-09-27 18:26 ` Simon Glass
2011-09-27 17:56 ` Tim Bird
2011-09-27 17:56 ` Tim Bird
2011-09-27 17:57 ` Tim Bird
2011-09-27 17:57 ` Tim Bird
2011-09-27 18:42 ` Simon Glass
2011-09-27 18:42 ` Simon Glass
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4E802F7D.9000006@parrot.com \
--to=matthieu.castet@parrot.com \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.