Re: [PATCH] slow_work_thread() should do the exclusive wait
From: David Howells
Date: Thu Apr 16 2009 - 05:11:20 EST
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> The patch itself is a little worrisome. The wake-all semantics are
> very good at covering up little race bugs. And switching to wake-once
> is a great way of exposing hitherto-unsuspected races.
It's something I'm intending to test, once I get MN10300 working again (which
for some reason it isn't).
> I wonder if slow_work_cull_timeout() should have some sort of barrier,
> so the write is suitably visible to the woken thread.
That's an interesting question. Should wake_up() imply a barrier of any sort,
I wonder. Well, __wake_up() does impose a barrier as it uses a spinlock, but
I wonder if that's sufficient.
> Bearing in mind that the thread might _already_ have been woken by someone
> else?
If the thread is woken by someone else, there must be work for it to do, in
which case it wouldn't be culled anyway.
> off-topic: afacit the code will cull a maximum of one thread per five
> seconds. But the rate of thread _creation_ is, afacit, unbound. Are
> there scenarios in which we can get a runaway thread count?
The maximum number of threads is limited (slow_work_max_threads).
David
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