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 16:57:41 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        "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

On Wed, 16 Aug 2017, Luck, Tony wrote:
> > 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?

Don't think so. It was just a thought, but the code as provided is fine and
merged as is.

Thanks,

	tglx