On Tue, Jul 05, 2016 at 10:35:26AM +0200, Peter Zijlstra wrote: > On Mon, Jul 04, 2016 at 07:05:35PM +0100, Mark Rutland wrote: > > On Sat, Jul 02, 2016 at 06:40:25PM +0200, Peter Zijlstra wrote: > > > One of the ways I was looking at getting that done is a virtual runtime > > > scheduler (just like cfs). The tricky point is merging two virtual > > > runtime trees. But I think that should be doable if we sort the trees on > > > lag. > > > > > > In any case, the relevance to your question is that once we have a tree, > > > we can play games with order; that is, if we first order on PMU-id and > > > only second on lag, we get whole subtree clusters specific for a PMU. > > > > Hmm... I'm not sure how that helps in this case. Wouldn't we still need > > to walk the sibling list to get the HW PMU-id in the case of a SW group > > leader? > > Since there is a hardware even in the group, it must be part of the > hardware pmu list/tree and would thus end up classified (and sorted) by > that (hardware) PMU-id. > > > For the heterogeenous case we'd need a different sort order per-cpu > > (well, per microarchitecture), which sounds like we're going to have to > > fully sort the events every time they move between CPUs. :/ > > Confused, I thought that for the HG case you had multiple events, one > for each PMU. If we classify these events differently we'd simply use a > different subtree depending on which CPU the task lands.
My bad; I assumed that for both PMUs we'd start at the root, and thus would need to re-sort in order to get the current CPU's PMU ordered first, much like currently with rotation. I guess I'm having difficulty figuring out the structure of that tree. If we can easily/cheaply find the relevant sub-tree then the above isn't an issue. > Currently we've munged the two PMUs together, because, well, that's the > only way. Yeah. Splitting them by any means would be great. In the past I'd looked at changing task_struct::perf_event_ctxp into something that could handle an arbitrary number of contexts, such that we could avoid sharing, but ran away after considering the locking/rcu implications. Thanks, Mark.
