On 03/30/2016 05:21 PM, Peter Zijlstra wrote: > On Wed, Mar 30, 2016 at 05:17:29PM +0200, Sebastian Andrzej Siewior wrote: >> On 03/30/2016 05:07 PM, Peter Zijlstra wrote: >>> On Wed, Mar 30, 2016 at 04:53:05PM +0200, Daniel Wagner wrote: >>>> From: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx> >>>> >>>> Completions have no long lasting callbacks and therefore do not need >>>> the complex waitqueue variant. Use simple waitqueues which reduces >>>> the contention on the waitqueue lock. >>> >>> Changelog really should have talk about the determinism thing. The last >>> time you posted this the point was raised that we should wake the >>> highest prio waiter in the defer case, you did not address this. >> >> So we really want to go this road? > > Dunno, but at least mention why it wouldn't matter. It seems I put to much effort into the cover letter. I should have spent that time in the changelog. Anyway, I am going through the users of complete_all() and it looks like most of them are either some setup code paths and the other bunch of calls are just making sure the single waiter really wakes up. >> I didn't find any numbers what the >> highest count of queued sleepers was in Daniel's complete_all() testing. >> >> As for the latest -RT I received only one report from Clark Williams >> with something like 3 to 9 sleepers waked up during one complete_all() >> and this happens in the resume code. >> Based on this, deferring wake-ups from IRQ-context and a RB-tree (or >> something like that for priority sorting) looks like a lot of complexity >> and it does not look like we gain much. > > Sure, but that equally puts the whole defer thing into question, if we > can put a hard cap on the max number (and WARN when exceeded) we're also > good. > >>> Also, you make no mention of the reduction of UINT_MAX to USHORT_MAX and >>> the implications of that. >> >> Wasn't this >> |To avoid a size increase of struct completion, I spitted the done >> |field into two half. >> >> later he mentions that we can't have 2M sleepers anymore. > > That wasn't in this changelog, therefore it wasn't read ;-) Got it, next version has all info in the changelog and not in the cover letter. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
