Re: NO_HZ migration of TCP ack timers

[David Miller]

From: Anton Blanchard <anton@xxxxxxxxx>
Date: Thu, 18 Feb 2010 16:28:20 +1100

> I think the problem is the CPU is most likely to be idle when an rx networking
> interrupt comes in. It seems the wrong thing to do to migrate any ack timers
> off the current cpu taking the interrupt, and with enough networks we train
> wreck transferring everyones ack timers to the nohz load balancer cpu. 

This migration against the very design of all of the TCP timers in the
tree currently.

For TCP, even when the timer is no longer needed, we don't cancel the
timer.  We do this in order to avoid touching the timer for the cancel
from a cpu other than the one the timer was scheduled on.

The timer therefore is always accessed, cache hot, locally to the cpu
where it was scheduled.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/