Re: [PATCH 08/21] x86/intel_rdt/cqm: Add RMID(Resource monitoring ID) management

From: Tony Luck
Date: Wed Jul 05 2017 - 13:59:58 EST

> In case that a RMID was never used on a particular package, the state check
> forces an IPI on all packages unconditionally. That's suboptimal at least.
> We know on which package a given RMID was used, so we could restrict the
> checks to exactly these packages, but I'm not sure it's worth the
> trouble. We might at least document that and explain why this is
> implemented in that way.

We only allocate RMIDs when a user makes a directory. I don't think
we should consider options that slow down context switch in order to
keep track of which packages were used just to make mkdir(2) a bit faster
in the case where we need to check the limbo list.

We could make the check of the limbo list less costly by using a bitmask
to keep track of which packages have already found that the llc_occupancy
is below the threshold. But I'd question whether the extra complexity in the
code was really worth it.

-Tony [on vacation - responses will be slow]