linux-kernel - Re: radeon breaks with clocksource

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Date:	Fri, 23 Feb 2007 14:13:07 -0800
From:	"john stultz" <johnstul@...ibm.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: radeon breaks with clocksource_jiffies

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

On 2/23/07, john stultz <johnstul@...ibm.com> wrote:
> On 2/23/07, David Miller <davem@...emloft.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
>
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