Messages in this thread | | | Date | Tue, 10 Apr 2007 04:33:57 -0400 | From | Jeff Garzik <> | Subject | Re: init's children list is long and slows reaping children. |
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Andrew Morton wrote: > On Tue, 10 Apr 2007 03:05:56 -0400 Jeff Garzik <jeff@garzik.org> wrote: > >> My main >> worry with keventd is that we might get stuck behind an unrelated >> process for an undefined length of time. > > I don't think it has ever been demonstrated that keventd latency is > excessive, or a problem. I guess we could instrument it and fix stuff > easily enough.
It's simple math, combined with user expectations.
On a 1-CPU or 2-CPU box, if you have three or more tasks, all of which are doing hardware reset tasks that could take 30-60 seconds (realistic for libata, SCSI and network drivers, at least), then OBVIOUSLY you have other tasks blocked for that length of time.
Since the cause of the latency is msleep() -- the entire reason why the driver wanted to use a kernel thread in the first place -- it would seem to me that the simple fix is to start a new thread, possibly exceeding the number of CPUs in the box.
> The main problem with keventd has been flush_scheduled_work() deadlocks: the
That's been a problem in the past, yes, but a minor one.
I'm talking about a key conceptual problem with keventd.
It is easy to see how an extra-long tg3 hardware reset might prevent a disk hotplug event from being processed for 30-60 seconds. And as hardware gets more complex -- see the Intel IOP storage card which runs Linux -- the reset times get longer, too.
So the issue is /not/ deadlocks.
> The thing to concentrate on here is the per-cpu threads, which is where the > proliferation appears to be coming from.
Strongly agreed.
Jeff
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