Re: [PATCH 2.6]: Make packet scheduler clock source configurable

[Patrick McHardy <kaber@trash.net>]

David S. Miller wrote:
> We can't use this stuff on Alpha, it's cycle counter overflows after
> just 10 minutes.  It works very strangely, something like only the
> lower 32-bits are guarenteed to be continually incrementing.

The code (although racy) can handle 32-bit cycle counters. get_cycles()
on alpha returns a 32-bit value, so psched_tick calls PSCHED_GET_TIME
to adjust psched_time_base once a second. It is basically the same as
before. This is the second condition for this too work, besides
get_cycles() incrementing at >1MHz, it needs to return either a 32-bit
value and really use the full 32 bit or return something bigger, which
is assumed not to overflow. Alpha seems to satisfy both conditions.

> I'm going to apply your patch and delete the Alpha parts.
> Meanwhile, ping Richard Henderson (rth@redhat.com) or one
> of the other Alpha experts for me to get confirmation on
> this stuff.

Even better.

Regards
Patrick