On Wed, Apr 17, 2013 at 09:08:17PM +0200, Daniel Vetter wrote:
> On Wed, Apr 10, 2013 at 12:28 AM, Steven Rostedt wrote:
> > On Thu, Apr 04, 2013 at 06:41:02PM +0200, Peter Zijlstra wrote:
> >> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> >> > The thing is now that you're not expected
On Wed, Apr 10, 2013 at 12:28 AM, Steven Rostedt wrote:
> On Thu, Apr 04, 2013 at 06:41:02PM +0200, Peter Zijlstra wrote:
>> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
>> > The thing is now that you're not expected to hold these locks for a
>> > long
>> > time - if you need to synchro
On Mon, Apr 08, 2013 at 01:50:26PM +0200, Daniel Vetter wrote:
> On Mon, Apr 08, 2013 at 12:39:24PM +0200, Peter Zijlstra wrote:
> > On Thu, 2013-04-04 at 18:56 +0200, Daniel Vetter wrote:
> > > Presuming I'm still following we should be able to fix this with the
> > > new sleep state TASK_DEADLOCK
On Tue, Apr 09, 2013 at 06:28:08PM -0400, Steven Rostedt wrote:
> On Thu, Apr 04, 2013 at 06:41:02PM +0200, Peter Zijlstra wrote:
> > On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> > > The thing is now that you're not expected to hold these locks for a
> > > long
> > > time - if you need
On Wed, Apr 10, 2013 at 12:27 AM, Steven Rostedt wrote:
> On Thu, Apr 04, 2013 at 06:38:36PM +0200, Peter Zijlstra wrote:
>> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
>> > Hm, I guess your aim with the TASK_DEADLOCK wakeup is to bound the
>> > wait
>> > times of older task.
>>
>> No,
On Tue, 2013-04-09 at 18:42 -0400, Steven Rostedt wrote:
> What about setting an age as soon as it starts the process
> of grabbing one of these locks? And it keeps the age until it
> successfully grabs and releases all the locks again. It wont reset if
> it
> had to drop the locks and start over.
On Thu, Apr 04, 2013 at 06:56:58PM +0200, Daniel Vetter wrote:
>
> I think for starters we need to have a slightly more interesting example:
>
> 3 threads O, M, Y: O has the oldest ww_age/ticket, Y the youngest, M
> is in between.
> 2 ww_mutexes: A, B
>
> Y has already acquired ww_mutex A, M has
On Thu, Apr 04, 2013 at 06:41:02PM +0200, Peter Zijlstra wrote:
> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> > The thing is now that you're not expected to hold these locks for a
> > long
> > time - if you need to synchronously stall while holding a lock
> > performance
> > will go d
On Thu, Apr 04, 2013 at 06:38:36PM +0200, Peter Zijlstra wrote:
> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> > Hm, I guess your aim with the TASK_DEADLOCK wakeup is to bound the
> > wait
> > times of older task.
>
> No, imagine the following:
>
> struct ww_mutex A, B;
> struct mute
On Tue, Apr 02, 2013 at 06:59:14PM +0200, Peter Zijlstra wrote:
>
> So how about we call the thing something like:
>
> struct ww_mutex; /* wound/wait */
Reading this I can't help but think of Elmer Fudd saying "Round Robin"
as "Wound Wobin"
-- Steve
>
> int mutex_wound_lock(struct ww_mute
On Mon, Apr 08, 2013 at 12:39:24PM +0200, Peter Zijlstra wrote:
> On Thu, 2013-04-04 at 18:56 +0200, Daniel Vetter wrote:
> > Presuming I'm still following we should be able to fix this with the
> > new sleep state TASK_DEADLOCK and a flag somewhere in the thread info
> > (let's call it PF_GTFO for
On Thu, 2013-04-04 at 18:56 +0200, Daniel Vetter wrote:
> On Thu, Apr 4, 2013 at 3:31 PM, Daniel Vetter wrote:
> >> In this case when O blocks Y isn't actually blocked, so our
> >> TASK_DEADLOCK wakeup doesn't actually achieve anything.
> >>
> >> This means we also have to track (task) state so th
On Thu, Apr 4, 2013 at 6:49 PM, Peter Zijlstra wrote:
> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
>> We've discussed this approach of using (rt-prio, age) instead of just
>> age
>> to determine the the "oldness" of a task for deadlock-breaking with
>> -EAGAIN. The problem is that thr
On Thu, Apr 4, 2013 at 6:38 PM, Peter Zijlstra wrote:
> On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
>> Hm, I guess your aim with the TASK_DEADLOCK wakeup is to bound the
>> wait
>> times of older task.
>
> No, imagine the following:
>
> struct ww_mutex A, B;
> struct mutex C;
>
>
On Thu, Apr 4, 2013 at 3:31 PM, Daniel Vetter wrote:
>> In this case when O blocks Y isn't actually blocked, so our
>> TASK_DEADLOCK wakeup doesn't actually achieve anything.
>>
>> This means we also have to track (task) state so that once Y tries to
>> acquire A (creating the actual deadlock) we'
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> Well, it was a good read and I'm rather happy that we agree on the
> ww_ctx
> thing (whatever it's called in the end), even though we have slightly
> different reasons for it.
Yeah, I tried various weirdness to get out from under it, but th
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> We've discussed this approach of using (rt-prio, age) instead of just
> age
> to determine the the "oldness" of a task for deadlock-breaking with
> -EAGAIN. The problem is that through PI boosting or normal rt-prio
> changes
> while tasks ar
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> I'm a bit confused about the different classes you're talking about.
> Since
> the ticket queue is currently a global counter there's only one class
> of
> ww_mutexes.
Right, so that's not something that's going to fly.. we need to support
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> Another big reason for having a start/end marker like you've describe
> is
> lockdep support.
Yeah, I saw how you did that.. but there's other ways of making it work
too, you could for instance create a new validation state for this type
of
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> The thing is now that you're not expected to hold these locks for a
> long
> time - if you need to synchronously stall while holding a lock
> performance
> will go down the gutters anyway. And since most current
> gpus/co-processors
> still
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> The trick with the current code is that the oldest task
> will never see an -EAGAIN ever and hence is guaranteed to make forward
> progress. If the task is really unlucky though it might be forced to
> wait
> for a younger task for every ww_
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> Hm, I guess your aim with the TASK_DEADLOCK wakeup is to bound the
> wait
> times of older task.
No, imagine the following:
struct ww_mutex A, B;
struct mutex C;
task-O task-Y task-X
A
B
On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> We do add some form of owner tracking by storing the reservation
> ticket
> of the current holder into every ww_mutex. So when task-Y in your
> above
> example tries to acquire lock A it notices that it's behind in the
> global
> queue and i
On Thu, Apr 04, 2013 at 02:01:48PM +0200, Peter Zijlstra wrote:
>
> I'm sorry, this email ended up quite a bit longer than I had hoped for;
> please bear with me.
>
> On Tue, 2013-04-02 at 18:59 +0200, Peter Zijlstra wrote:
> > struct ww_mutex; /* wound/wait */
> >
> > int mutex_wound_lock(s
I'm sorry, this email ended up quite a bit longer than I had hoped for;
please bear with me.
On Tue, 2013-04-02 at 18:59 +0200, Peter Zijlstra wrote:
> struct ww_mutex; /* wound/wait */
>
> int mutex_wound_lock(struct ww_mutex *); /* returns -EDEADLK */
> int mutex_wait_lock(struct ww_mute
On Tue, Apr 2, 2013 at 6:59 PM, Peter Zijlstra wrote:
>> > Also, is there anything in CS literature that comes close to this? I'd
>> > think the DBMS people would have something similar with their
>> > transactional systems. What do they call it?
>
>> I didn't study cs, but judging from your phras
On Tue, Apr 2, 2013 at 6:59 PM, Peter Zijlstra wrote:
>> > Head hurts, needs more time to ponder. It would be good if someone else
>> > (this would probably be you maarten) would also consider this explore
>> > this 'interesting' problem space :-)
>
>> My head too, evil priority stuff!
>>
>> Hacky
On Tue, 2013-04-02 at 16:57 +0200, Maarten Lankhorst wrote:
> Hey,
>
> Thanks for reviewing.
Only partway through so far :-)
> Op 02-04-13 13:00, Peter Zijlstra schreef:
> > On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
> >> +Reservation type mutexes
> >> +struct ticket_mutex {
> >
On Tue, Apr 2, 2013 at 1:00 PM, Peter Zijlstra wrote:
> Also, is there anything in CS literature that comes close to this? I'd
> think the DBMS people would have something similar with their
> transactional systems. What do they call it?
I've looked around a bit and in dbms row-locking land this
Hey,
Thanks for reviewing.
Op 02-04-13 13:00, Peter Zijlstra schreef:
> On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
>> +Reservation type mutexes
>> +struct ticket_mutex {
>> +extern int __must_check _mutex_reserve_lock(struct ticket_mutex *lock,
> That's two different names and tw
On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
> +The algorithm that TTM came up with for dealing with this problem is
> +quite simple. For each group of buffers (execbuf) that need to be
> +locked, the caller would be assigned a unique reservation_id, from a
> +global counter. In ca
On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
> +Reservation type mutexes
> +struct ticket_mutex {
> +extern int __must_check _mutex_reserve_lock(struct ticket_mutex *lock,
That's two different names and two different forms of one (for a total
of 3 variants) for the same scheme.
F
On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
> +struct ticket_mutex {
> + struct mutex base;
> + atomic_long_t reservation_id;
> +};
I'm not sure this is a good name, esp. due to the potential confusion
vs the ticket spinlocks we have.
--
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On Thu, 2013-02-28 at 11:25 +0100, Maarten Lankhorst wrote:
> +mutex_reserve_lock_slow and mutex_reserve_lock_intr_slow:
> + Similar to mutex_reserve_lock, except it won't backoff with
> -EAGAIN.
> + This is useful when mutex_reserve_lock failed with -EAGAIN, and you
> + unreserved all reservati
New version. All of the documentation has been moved from the commit log to
Documentation/reservation-mutex-design.txt
Missing at the moment, maybe TODO?
Add a lockdep check in the *_slow calls that verifies that the lock
being nested into has no nested lock any more? This would be a check
to mak
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