Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1243743

Re: [PATCH] sched_clock: add data pointer argument to read callback

Show all headers | View raw

On Sat, Oct 10, 2015 at 12:48:22AM +0100, Måns Rullgård wrote:
> Russell King - ARM Linux <linux@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.

-- 
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [PATCH] sched_clock: add data pointer argument to read callback Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-10 01:30 +0200
  Re: [PATCH] sched_clock: add data pointer argument to read callback Måns Rullgård <mans@mansr.com> - 2015-10-10 01:50 +0200
    Re: [PATCH] sched_clock: add data pointer argument to read callback Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-10 02:00 +0200
      Re: [PATCH] sched_clock: add data pointer argument to read callback Måns Rullgård <mans@mansr.com> - 2015-10-10 02:50 +0200
        Re: [PATCH] sched_clock: add data pointer argument to read callback Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-10 17:40 +0200

csiph-web