Messages in this thread | | | Date | Fri, 9 Jan 2015 16:58:35 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs |
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On Fri, Jan 09, 2015 at 03:24:42PM +0000, Matt Fleming wrote: > On Fri, 09 Jan, at 02:02:50PM, Peter Zijlstra wrote: > > On Fri, Jan 09, 2015 at 12:14:01PM +0000, Matt Fleming wrote: > > > On Tue, 06 Jan, at 06:17:12PM, Peter Zijlstra wrote: > > > > > > > > afaict the again label will try and steal yet another rmid, if rmids > > > > don't decay fast enough, we could end up with all rmids on the limbo > > > > list and none active. Or am I missing something here? > > > > > > You're not missing anything, that's true, we will try and steal more > > > RMIDs. We could perhaps put a limit on how many RMIDs we're willing to > > > steal, but I think it should definitely be > 1 because RMIDs can > > > stabilize out of order. > > > > > > It's worth pointing out that we only steal more RMIDs if the ones on the > > > limbo list have been queued for the "minimum queue time" - it really is > > > a last resort. > > > > Do we really care? Why not just hold up everything until the one(s) we > > have are low enough? > > > > Yes it all blows, but would not some active be better than none active, > > just because the stupid lines aren't clearing fast enough? > > Right, but now we need a "steal limit", so we know when to stop stealing > active RMIDs. > > (cqm_max_rmid + 1) / 4 ? > > I guess any limit is better than no limit.
Yeah, that'll work, when the free+limbo count is 1/4th the total we should stop pulling more plugs.
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