Re: [PATCH] CPU hotplug: Slow down hotplug operations

[Andrew Morton <akpm@linux-foundation.org>]

On Wed,  7 May 2014 21:57:41 +0200 Borislav Petkov <bp@alien8.de> wrote:

> We have all those eager tester dudes which scratch up a dirty script to
> pound on CPU hotplug senselessly and then report bugs they've managed to
> trigger.
> 
> Well, first of all, most, if not all, bugs they trigger are CPU hotplug
> related anyway. But we know hotplug is full of duct tape and brown
> paper bags. So we end up clearly wasting too much time dealing with a
> mechanism we know it is b0rked in the first place.
> 
> Oh, and I would understand if that pounding were close to some real
> usage patterns but I've yet to receive a justification for toggling
> cores on- and offline senselessly.
> 
> In any case, before this gets rewritten properly (I'm being told we
> might get lucky after all) let's slow down hotplugging on purpose and
> thus make it uninteresting, as a temporary brown paper bag solution
> until the real thing gets done.
> 
> This way we'll save us a lot of time and efforts in chasing the wrong
> bugs.

Well, I only yesterday merged Srivatsa's `CPU hotplug, stop-machine:
plug race-window that leads to "IPI-to-offline-CPU"' bugfix.  That bug
presumably wouldn't have been fixed if this patch was in place.