Re: radeon breaks with clocksource_jiffies

["john stultz" <johnstul@us.ibm.com>]

Crud, my poor gmail skills dropped lkml on the CC list for this one.

On 2/23/07, john stultz <johnstul@us.ibm.com> wrote:
> On 2/23/07, David Miller <davem@davemloft.net> wrote:
> > While probeing PLL information via radeon_get_pllinfo(), it does a
> > "gettimeofday(); do_something(); gettimeofday();" type sequence
> > explicitly with interrupts disabled, so ends up with a zero
> > measurement which then results in a bunch of divisions by zero.
>
> This is at module init time?  If so I just sent out a patch yesterday
> to akpm that might help this issue (assuming other clocksources are
> available on the hardware).
>
>
> > We should decide whether gettimeofday() can be expected to advance with
> > interrupts disabled, or that clocksource_jiffies is simply invalid because
> > of this behavior.
>
> Some arches have no fine-grained timekeeping, so I don't think it can
> always be assumed, but where hardware is available it should function.
>
> It should be noted that with older kernels, if interrupts were
> disabled right before a tick, it would be possible that
> gettimeofday()'s limiting code would cause time to stop advancing
> until interrupts were re-enabled. So theoretically its not really a
> new issue.
>
> The timekeeping_is_continuous() function could be used to flag this
> sort of "software driven vs continuous" clocksource cases.
>
> thanks
> -john
>