From: Tim Hockin <thockin@hockin.org>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: Rusty Russell <rusty@au1.ibm.com>,
vatsa@in.ibm.com, linux-kernel@vger.kernel.org,
torvalds@osdl.org, akpm@osdl.org, rml@tech9.net
Subject: Re: CPU Hotplug: Hotplug Script And SIGPWR
Date: Mon, 19 Jan 2004 23:54:09 -0800 [thread overview]
Message-ID: <20040120075409.GA13897@hockin.org> (raw)
In-Reply-To: <400CDCA1.5070200@cyberone.com.au>
On Tue, Jan 20, 2004 at 06:45:37PM +1100, Nick Piggin wrote:
> >I guess a hotplug script MAY fail. I don't think it's a good idea to make
> >your CPU hotplug script fail. May and Misght are different. It's up to
> >the
> >implementor whether the script can get into a failure condition.
> >
>
> Sorry bad wording. The script may fail to be executed.
Under what conditions? Not arbitrary entropy, surely. If a hotplug script
is present and does not blow up, it should be safe to assume it will be run
upon an event being delivered. If not, we have a WAY bigger problem :)
> >What if <which> process needs guaranteed scheduling latency? Do we really
> >_guarantee_ scheduling latency *anywhere*?
>
> We do guarantee that a realtime task won't be blocked waiting for
> a hotplug script to fault in and start it up again (which may not
> happen). Not sure how important this issue is.
We have a conflict of priority here. If an RT task is affined to CPU A and
CPU A gets yanked out, what do we do?
Obviously the RT task can't keep running as it was. It was affined to A.
Maybe for a good reason. I see we have a few choices here:
* re-affine it automatically, thereby silently undoing the explicit
affinity.
* violate it's RT scheduling by not running it until it has been re-affined
or CPU A returns to the pool/
Sending it a SIGPWR means you have to run it on a different CPU that it was
affined to, which is already a violation.
Basically, RT tasks + CPU affinity + hotplug CPUs do not play nicely
together. I don't see much that can be done to solve that. With the
procstate stuff I did, and with planned CPU unplugs we *do* have time before
the CPU really goes offline in which to act. With unplanned CPU offlining,
we don't.
next prev parent reply other threads:[~2004-01-20 7:54 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20040116174446.A2820@in.ibm.com>
2004-01-20 5:44 ` CPU Hotplug: Hotplug Script And SIGPWR Rusty Russell
2004-01-20 6:33 ` Tim Hockin
2004-01-20 6:43 ` Nick Piggin
2004-01-20 6:52 ` Tim Hockin
2004-01-20 7:11 ` Nick Piggin
2004-01-20 7:30 ` Tim Hockin
2004-01-20 7:45 ` Nick Piggin
2004-01-20 7:54 ` Tim Hockin [this message]
2004-01-20 8:14 ` Nick Piggin
2004-01-20 8:29 ` Tim Hockin
2004-01-20 8:37 ` Nick Piggin
2004-01-20 8:43 ` Tim Hockin
2004-01-21 4:06 ` Srivatsa Vaddagiri
2004-01-21 4:14 ` Nick Piggin
2004-01-21 5:09 ` Srivatsa Vaddagiri
2004-01-21 7:08 ` Tim Hockin
2004-01-21 15:07 ` Matthias Urlichs
2004-01-22 5:29 ` Rusty Russell
2004-01-21 7:09 ` Tim Hockin
2004-01-21 7:31 ` Nick Piggin
2004-01-21 7:42 ` Tim Hockin
2004-01-21 8:11 ` Rusty Russell
2004-01-21 5:07 ` Rusty Russell
2004-01-20 8:41 ` Stefan Smietanowski
2004-01-20 8:49 ` Nick Piggin
2004-01-20 9:12 ` Tim Hockin
2004-01-21 0:00 ` Rusty Russell
2004-01-20 23:51 ` Rusty Russell
2004-01-20 7:45 ` Rusty Russell
2004-01-20 8:37 ` Tim Hockin
2004-01-20 9:29 ` Srivatsa Vaddagiri
2004-01-21 0:12 ` Rusty Russell
[not found] <fa.f37o48p.1io5q5@ifi.uio.no>
[not found] ` <fa.frjqvfo.170g8hq@ifi.uio.no>
2004-01-20 17:49 ` Andy Lutomirski
2004-01-21 4:33 ` Rusty Russell
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