Messages in this thread | | | Date | Mon, 26 Jan 2009 23:25:19 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2/3] work_on_cpu: Use our own workqueue. |
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On Tue, 27 Jan 2009 17:35:11 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:
> On Monday 26 January 2009 17:31:30 Andrew Morton wrote: > > On Mon, 26 Jan 2009 17:11:43 +1030 Rusty Russell <rusty@rustcorp.com.au> 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.
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