linux-kernel - Re: [PATCH RFC 0/8] Dynamic clock devices

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Date:	Mon, 08 Nov 2010 15:01:04 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 0/8] Dynamic clock devices

On Thu, 2010-11-04 at 20:26 +0100, Richard Cochran wrote:
> The clock_ syscalls are moved into a new file and they call the older
> posix functions when needed. The timer_ syscalls stay where they are,
> in posix-timers.c, since I did not want to change the fairly involved
> timer management code. Eventually, we could remove the posix clock_*
> functions for the CLOCK_* ids from posix-timers.c and rework them
> using the new dynamic clock api. That would leave just the timer code
> in posix-timers.c, as the file name suggests.
> 
> I dropped the idea of having user space open a sysfs file in order to
> get a reference to a clock, since there are no open/release hooks
> within sysfs for drivers (coincidentally, there has been some talk
> about this on the lkml recently, but previously Greg KH object to
> abusing sysfs as a "clockfs").
> 
> Instead, since many clocks (hpet, rtc, ptp, ...) will want to offer a
> custom chardev for special advanced functionality, the dynamic clock
> layer registers a cdev for the driver, placing its own hooks into the
> open/release methods. The driver thus needs to access its private data
> via a standard access method (not just by using fp->private_data). If
> a driver doesn't want any chardev functions, that is okay, too.
> 
> Well, please take a look and let me know what you think.

Hey Richard!
	Thanks for sending this patchset out for review! This is definitely a
larger redesign from your earlier patch, and I see now how the
per-thread cputime clockids throws a wrench in my argument just using
the incremental clockids that hash into a smaller array to avoid id
reuse.

That said, given how different this is from the last implementation, I'm
not fully clear I see how to integrate this into my patch set. It might
be useful to see a trivial example of how you see a clockdevice being
registered and used.

Overall it looks interesting, but there may be a few catches that we may
have to watch out for.

I have a few other comments I'll make in context of the patches to
follow shortly.

thanks again!
-john

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