linux-kernel - RE: [PATCH 1/2] x86/intel_rdt/mbm: Fix MBM overflow handler during hot cpu

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Date:   Wed, 16 Aug 2017 14:53:52 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>
CC:     "Shivappa, Vikas" <vikas.shivappa@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "davidcc@...gle.com" <davidcc@...gle.com>
Subject: RE: [PATCH 1/2] x86/intel_rdt/mbm: Fix MBM overflow handler during
 hot cpu

> You could alternatively use flush and make the worker code schedule the
> work on a still online CPU in the domain instead of blindly rescheduling it
> on the same CPU.

We looked at that when you suggested flush. The problem is that we have
already deleted the current cpu from the bitmask for the domain. So the
worker code doesn't know which domain it is running on, so can't pick
another.

If we try to do the flush before dropping the cpu from the bitmask, then
the worker code doesn't have any reason to pick a different CPU.

Is there is some cheap "I'm running on a CPU that is in the process of going
offline" test that we could make in the worker code?

-Tony