Re: [PATCH v3 4/4] kmod: throttle kmod thread limit

Luis R. Rodriguez
2017-06-23T19:16:43Z

On Fri, Jun 23, 2017 at 07:56:11PM +0200, Luis R. Rodriguez wrote:
> On Fri, Jun 23, 2017 at 06:16:19PM +0200, Luis R. Rodriguez wrote:
> > On Thu, Jun 22, 2017 at 05:19:36PM +0200, Petr Mladek wrote:
> > > On Fri 2017-05-26 14:12:28, Luis R. Rodriguez wrote:
> > > > --- a/kernel/kmod.c
> > > > +++ b/kernel/kmod.c
> > > > @@ -178,6 +175,7 @@ int __request_module(bool wait, const char *fmt, ...)
> > > > ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
> > > >
> > > > atomic_inc(&kmod_concurrent_max);
> > > > + wake_up_all(&kmod_wq);
> > >
> > > Does it make sense to wake up all waiters when we released the resource
> > > only for one? IMHO, a simple wake_up() should be here.
> >
> > Then we should wake_up() also on failure, otherwise we have the potential
> > to not wake some in a proper time.
>
> I checked and it turns out we have no error paths after we consume a kmod
> ticket, if you will. Once we bump with atomic_dec_if_positive() we assume
> we're moving forward with an attempt, and the only failure path is already
> bundled with a wake at the end of the __request_module() call.
>
> Then the next question would be *who* exactly gets woken up next if we just
> use wake_up() ? The common core wake up code varies depending on use and
> all this reminded me of the complexity we just don't need, so I have now
> converted to use swait. swait uses list_add() if empty and then iterates
> with list_first_entry() on wakeup, so that should get the first item added
> to the wait list.
>
> Works with me. Will run a test a before v4 is sent, but since only 2 patches
> are modified will only send a respective update for these 2 patches.

Alright, this worked out well! Its just a tiny bit slower on test cases 0008
and 0009 (few seconds) but that's fine, its natural due to the lack of the
swake_up_all().

Luis