* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Mon, 2011-06-06 at 18:08 +0200, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > > On Mon, 2011-06-06 at 17:52 +0200, Ingo Molnar wrote:
> > > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > >
> > > > > Needs more staring at, preferably by someone who actually
> > > > > understands that horrid mess :/ Also, this all still doesn't make
> > > > > printk() work reliably while holding rq->lock.
> > > >
> > > > So, what about my suggestion to just *remove* the wakeup from there
> > > > and use the deferred wakeup mechanism that klogd uses.
> > > >
> > > > That would make printk() *visibly* more robust in practice.
> > >
> > > That's currently done from the jiffy tick, do you want to effectively
> > > delay releasing the console_sem for the better part of a jiffy?
> >
> > Yes, and we already do it in some other circumstances.
>
> We do?
Yes, see the whole printk_pending logic, it delays:
wake_up_interruptible(&log_wait);
to the next jiffies tick.
> > Can you see
> > any problem with that? klogd is an utter slowpath anyway.
>
> but console_sem isn't klogd. We delay klogd and that's perfectly
> fine, but afaict we don't delay console_sem.
But console_sem is really a similar special case as klogd. See, it's
about a *printk*. That's rare by definition.
If someone on the console sees it he'll be startled by at least 10
msecs ;-) So delaying the wakeup to the next jiffy really fits into
the same approach as we already do with &log_wait, hm?
This would solve a real nightmare that has plagued us ever since
printk() has done wakeups directly - i.e. like forever.
Thanks,
Ingo
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