On Thu, Jun 29, 2017 at 09:40:15PM +0200, Luis R. Rodriguez wrote:

On Thu, Jun 29, 2017 at 11:59:29AM -0700, Linus Torvalds wrote:

quoted

On Thu, Jun 29, 2017 at 11:33 AM, Davidlohr Bueso [off-list ref] wrote:

quoted

On Thu, 29 Jun 2017, Linus Torvalds wrote:

quoted

I actually think swait is pure garbage. Most users only wake up one
process anyway, and using swait for that is stupid. If you only wake
up one, you might as well just have a single process pointer, not a
wait list at all, and then use "wake_up_process()".

But you still need the notion of a queue, even if you wake one task
at a time... I'm probably missing your point here.

The *reason* they wake up only one seems to be that there really is
just one. It's some per-cpu idle thread for kvm, and for RCU it's the
RCU workqueue thread.

So the queue literally looks suspiciously pointless.

But I might be wrong, and there can actually be multiple entries.

Since this swake_up() --> swake_up_all() reportedly *fixed* the one wake up
issue it would seem this does queue [0]. That said, I don't see any simple tests
tools/testing/selftests/swait but then again we don't have test for regular
waits either...

[0] https://bugzilla.kernel.org/show_bug.cgi?id=195477

I should also note that the swake_up_all() should have only helped in cases where
3 cards were used, as if only 2 were used that should have been covered by just
the swake_up(). Unless of course I hear otherwise by the reporter, Nicolas or
from Jakub.

  Luis