On 15.07.2005 [00:28:44 +0200], Roman Zippel wrote:
> Hi,
>
> On Thu, 14 Jul 2005, Nishanth Aravamudan wrote:
>
> > We no longer use jiffies (the variable) as the basis for determining
> > what "time" a timer should expire or when it should be added. Instead,
> > we use a new function, do_monotonic_clock(), which is simply a wrapper
> > for getnstimeofday().
>
> And suddenly a simple 32bit integer becomes a complex 64bit integer, which
> requires hardware access to read a timer and additional conversion into ns.
> Why is suddenly everyone so obsessed with molesting something simple and
> cute as jiffies?
Thanks for the feedback, Roman. I know the 64-bit operations are
critical from a performance perspective and may be excessive from a
pragmatic perspective. Maybe an alternative would be to only provide
*microsecond* resolution in the software, which I currently assume is
storable in an unsigned long (a little over an hour?). We could then
provide a supplemental interface for those sleeps which would exceed
this time, either via looping or a 64-bit parameter for this special
interface.
Would that perhaps be a better alternative from the 64-bit perspective?
We could do this one better, perhaps, by basically doing exactly what
jiffies does now, but storing a time value (in microseconds) instead of
a count of the number of ticks (jiffies' current interpretation). This
would perhaps be a 64-bit op, but that is the case current with
jiffies_64++ (or jiffies_64 += jiffies_increment). I will work on some
patches to do something to this effect and will bring it up during the
time/timer talk (Saturday at 13h30).
Thanks again,
Nish
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