[PATCH] sched_clock: add data pointer argument to read callback
Russell King - ARM Linux
linux at arm.linux.org.uk
Sat Oct 10 08:33:36 PDT 2015
On Sat, Oct 10, 2015 at 01:42:47AM +0100, Måns Rullgård wrote:
> Russell King - ARM Linux <linux at arm.linux.org.uk> writes:
> > On Sat, Oct 10, 2015 at 12:48:22AM +0100, Måns Rullgård wrote:
> >> Russell King - ARM Linux <linux at arm.linux.org.uk> writes:
> >> > On Fri, Oct 09, 2015 at 10:57:35PM +0100, Mans Rullgard wrote:
> >> >> This passes a data pointer specified in the sched_clock_register()
> >> >> call to the read callback allowing simpler implementations thereof.
> >> >>
> >> >> In this patch, existing uses of this interface are simply updated
> >> >> with a null pointer.
> >> >
> >> > This is a bad description. It tells us what the patch is doing,
> >> > (which we can see by reading the patch) but not _why_. Please include
> >> > information on why the change is necessary - describe what you are
> >> > trying to achieve.
> >> Currently most of the callbacks use a global variable to store the
> >> address of a counter register. This has several downsides:
> >> - Loading the address of a global variable can be more expensive than
> >> keeping a pointer next to the function pointer.
> >> - It makes it impossible to have multiple instances of a driver call
> >> sched_clock_register() since the caller can't know which clock will
> >> win in the end.
> >> - Many of the existing callbacks are practically identical and could be
> >> replaced with a common generic function if it had a pointer argument.
> >> If I've missed something that makes this a stupid idea, please tell.
> > So my next question is whether you intend to pass an iomem pointer
> > through this, or a some kind of structure, or both. It matters,
> > because iomem pointers have a __iomem attribute to keep sparse
> > happy. Having to force that attribute on and off pointers is frowned
> > upon, as it defeats the purpose of the sparse static checker.
> So this is an instance where tools like sparse get in the way of doing
> the simplest, most efficient, and obviously correct thing. Who wins in
> such cases?
In that case, NAK on the patch. I don't have time for your stupid games.
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