On Sat, Jul 02, 2016 at 06:40:25PM +0200, Peter Zijlstra wrote: > On Tue, Jun 14, 2016 at 04:10:41PM +0100, Mark Rutland wrote: > > However, pmu::filter_match is only called for the leader of each event > > group. When the leader is a SW event, we do not filter the groups, and > > may fail at pmu::add time, and when this happens we'll give up on > > scheduling any event groups later in the list until they are rotated > > ahead of the failing group. > > Ha! indeed. > > > I've tried to find a better way of handling this (without needing to walk > > the > > siblings list), but so far I'm at a loss. At least it's "only" O(n) in the > > size > > of the sibling list we were going to walk anyway. > > > > I suspect that at a more fundamental level, I need to stop sharing a > > perf_hw_context between HW PMUs (i.e. replace task_struct::perf_event_ctxp > > with > > something that can handle multiple HW PMUs). From previous attempts I'm not > > sure if that's going to be possible. > > > > Any ideas appreciated! > > So I think I have half-cooked ideas. > > One of the problems I've been wanting to solve for a long time is that > the per-cpu flexible list has priority over the per-task flexible list. > > I would like them to rotate together.
Makes sense. > 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? 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. :/ > Lost of details missing in that picture, but I think something along > those lines might get us what we want. Perhaps! Hopefully I'm just missing those detail above. :) I also had another though about solving the SW-led group case: if the leader had a reference to the group's HW PMU (of which there should only be one), we can filter on that alone, and can also use that in group_sched_in rather than the ctx->pmu, avoiding the issue that ctx->pmu is not the same as the group's HW PMU. I'll have a play with that approach in the mean time. Thanks, Mark.
