missing RELOC()s in prom.c?

David Boutcher boutcher at us.ibm.com
Sat Feb 7 14:20:46 EST 2004

Anton Blanchard <anton at samba.org> wrote on 02/06/2004 07:57:28 PM:
> Speaking of things in the paca, does anyone know why we a) have an
> option to overclock the decr and b) have an option to overclock the
> decr on cpu0 separately? If its an issue with iseries servicing
> events, does the current HZ=1000 solve this?

Cause on legacy iSeries there are no real interrupts.  There are only lp
events put on a queue.  And we check the queue on each decrementer.  And
there's an option somewhere or other (search for spread_lp_events) for
whether we check the queue only with cpu0 or with all cpus..

By the way, at one point there was a cool option to stagger the
decrementers so that even with overclocking, multiple CPUs would check the
lp event queues at staggered intervals within the decrementer intervals.

Overclocking the decrementer doesn't do anything for jiffies, but it does
reduce the latency on I/O events and is only useful on legacy iSeries.

As to whether HZ helps, It's too late at night, and Hugh made me drink too
much beer to contemplate that.

Dave Boutcher
IBM Linux Technology Center

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