Messages in this thread | | | Date | Mon, 7 Jan 2013 20:27:50 -0800 | From | Srivatsa Vaddagiri <> | Subject | Re: [PATCH 1/2] cpuhotplug/nohz: Remove offline cpus from nohz-idle state |
| |
* Russell King - ARM Linux <linux@arm.linux.org.uk> [2013-01-05 10:36:27]:
> On Thu, Jan 03, 2013 at 06:58:38PM -0800, Srivatsa Vaddagiri wrote: > > I also think that the > > wait_for_completion() based wait in ARM's __cpu_die() can be replaced with a > > busy-loop based one, as the wait there in general should be terminated within > > few cycles. > > Why open-code this stuff when we have infrastructure already in the kernel > for waiting for stuff to happen? I chose to use the standard infrastructure > because its better tested, and avoids having to think about whether we need > CPU barriers and such like to ensure that updates are seen in a timely > manner.
I was primarily thinking of calling as few generic functions as possible on a dead cpu. I recall several "am I running on a dead cpu?" checks (cpu_is_offline(this_cpu) that were put in generic routines during early versions of cpu hotplug [1] to educate code running on dead cpu, the need for which went away though with introduction of atomic/stop-machine variant. The need to add a RCU_NONIDLE() wrapper around ARM's cpu_die() [2] is perhaps a more recent example of educating code running on dead cpu. As quickly we die as possible after idle thread of dying cpu gains control, the better!
1. http://lwn.net/Articles/69040/ 2. http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/107971.html
- vatsa -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
| |