Re: [PATCH v5 03/21] gpu: host1x: Show number of pending waiters in debugfs

Michał Mirosław
2021-04-01T21:21:01Z

On Fri, Mar 26, 2021 at 04:34:13PM +0200, Mikko Perttunen wrote:
> On 3/23/21 12:16 PM, Thierry Reding wrote:
> > On Mon, Jan 11, 2021 at 03:00:01PM +0200, Mikko Perttunen wrote:
> > > Show the number of pending waiters in the debugfs status file.
> > > This is useful for testing to verify that waiters do not leak
> > > or accumulate incorrectly.
> > >
> > > Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> > > ---
> > > drivers/gpu/host1x/debug.c | 14 +++++++++++---
> > > 1 file changed, 11 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/host1x/debug.c b/drivers/gpu/host1x/debug.c
> > > index 1b4997bda1c7..8a14880c61bb 100644
> > > --- a/drivers/gpu/host1x/debug.c
> > > +++ b/drivers/gpu/host1x/debug.c
> > > @@ -69,6 +69,7 @@ static int show_channel(struct host1x_channel *ch, void *data, bool show_fifo)
> > > static void show_syncpts(struct host1x *m, struct output *o)
> > > {
> > > + struct list_head *pos;
> > > unsigned int i;
> > > host1x_debug_output(o, "---- syncpts ----\n");
> > > @@ -76,12 +77,19 @@ static void show_syncpts(struct host1x *m, struct output *o)
> > > for (i = 0; i < host1x_syncpt_nb_pts(m); i++) {
> > > u32 max = host1x_syncpt_read_max(m->syncpt + i);
> > > u32 min = host1x_syncpt_load(m->syncpt + i);
> > > + unsigned int waiters = 0;
> > > - if (!min && !max)
> > > + spin_lock(&m->syncpt[i].intr.lock);
> > > + list_for_each(pos, &m->syncpt[i].intr.wait_head)
> > > + waiters++;
> > > + spin_unlock(&m->syncpt[i].intr.lock);
> >
> > Would it make sense to keep a running count so that we don't have to
> > compute it here?
>
> Considering this is just a debug facility, I think I prefer not adding a new
> field just for it.

This looks like IRQ-disabled region, so unless only root can trigger
this code, maybe the additional field could save a potential headache?
How many waiters can there be in the worst case?

Best Regards
Michał Mirosław