linux-kernel - Re: [git pull for -mm] CPU isolation extensions (updated2)

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Message-ID: <47B264E3.4090605@qualcomm.com>
Date:	Tue, 12 Feb 2008 19:32:51 -0800
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	David Miller <davem@...emloft.net>
CC:	nickpiggin@...oo.com.au, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, pj@....com, a.p.zijlstra@...llo.nl, gregkh@...e.de,
	rusty@...tcorp.com.au
Subject: Re: [git pull for -mm] CPU isolation extensions (updated2)

David Miller wrote:
> From: Nick Piggin <nickpiggin@...oo.com.au>
> Date: Tue, 12 Feb 2008 17:41:21 +1100
> 
>> stop machine is used for more than just module loading and unloading.
>> I don't think you can just disable it.
> 
> Right, in particular it is used for CPU hotplug.
Ooops. Totally missed that. And a bunch of other places.

[maxk@...2 cpuisol-2.6.git]$ git grep -l stop_machine_run
Documentation/cpu-hotplug.txt
arch/s390/kernel/kprobes.c
drivers/char/hw_random/intel-rng.c
include/linux/stop_machine.h
kernel/cpu.c
kernel/module.c
kernel/stop_machine.c
mm/page_alloc.c

I wonder why I did not see any issues when I disabled stop machine completely.
I mentioned in the other thread that I commented out the part that actually halts
the machine and ran it for several hours on my dual core laptop and on the quad
core server. Tried all kinds of workloads, which include constant module removal
and insertion, and cpu hotplug as well. It cannot be just luck :).

Clearly though, you guys are right. It cannot be simply disabled. Based on the 
above grep it's needed for CPU hotplug, mem hotplug, kprobes on s390 and intel
rng driver. Hopefully we can avoid it at least in module insertion/removal.

Max

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