Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.
From: Andrew Morton
Date: Tue Jan 27 2009 - 02:25:52 EST
On Tue, 27 Jan 2009 17:35:11 +1030 Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> On Monday 26 January 2009 17:31:30 Andrew Morton wrote:
> > On Mon, 26 Jan 2009 17:11:43 +1030 Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> >
> > > On Saturday 24 January 2009 18:45:37 Andrew Morton wrote:
> > > > Pity the poor reader who comes along trying to work out why this exists.
> >
> > (chirp, chirp)
>
> I disagree. It's simple; we create a workqueue and we use it. There's no
> confusion here.
Reader's first and most important question is "why does this exist".
> > > None of these options are appealing...
> >
> > Can we try harder please? 10 screenfuls of kernel threads in the ps
> > output is just irritating.
> >
> > How about banning the use of work_on_cpu() from schedule_work()
> > handlers and then fixing that driver somehow?
>
> Again, that's how we got here in the first place. I didn't realize the
> twisty path by which the acpi cpufreq code could be called. And there
> may well be others. So I want work_on_cpu to be completely generic.
But it isn't generic. The patch just moved the deadlock from one queue
to another. Making work_on_cu() truly generic is quite hard!
> But it's a general comment about fixing a general issue. The currently
> known case is not directly relevent; that it can happen and it's restricting
> the use of this otherwise-general API is.
I think we should switch acpi-cpufreq to smp_call_function(), revert
this stuff and ban the calling of work_on_cpu() under locks.
> A little confused at all this vitriol,
Well let's see.
- it was badly changelogged
- it was badly commented
- it's slow. In many ways, including the unnecessary serialisation
of each cross-cpu call in acpi-cpufreq.
- it consumes a tremendous amount of resources just to fix some
acpi locking snafu
- it adds yet another zillion kernel threads
- it's still deadlockable
- it got sent to Linus while still under active discussion
- and it got merged
- Oleg is the usual workqueue developer and wasn't even cc'ed.
- I am the usual workqueue reviewer/merger (and would prefer to remain
thus, please) and I wasn't cc'ed either.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/