linux-kernel - Re: [PATCH 8/8] x86/intel_rdt: rmdir,umount and hotcpu updates for MBA

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Date:   Mon, 23 Jan 2017 12:18:07 -0800 (PST)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        vikas.shivappa@...el.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, hpa@...or.com, mingo@...nel.org,
        peterz@...radead.org, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, h.peter.anvin@...el.com
Subject: Re: [PATCH 8/8] x86/intel_rdt: rmdir,umount and hotcpu updates for
 MBA

On Mon, 16 Jan 2017, Thomas Gleixner wrote:

> On Tue, 10 Jan 2017, Vikas Shivappa wrote:
>
>> During rmdir only reset the ctrl values for the rdtgroup's closid. This
>> is done so that that next time when the closid is reused they dont
>> reflect old values.
>
> How on earth is that related to MBA?

This is not specific to MBA so i put it as x86/intel_rdt in the subject but will 
send this as part of seperate series which you mentioned.

>
>> Remove the closid update during cpuonline in cqm as its
>> already in the CAT code. Since both cqm and CAT want the rmid and closid
>> to be zero when cpu is online, remove the PQR MSR write to zero during
>> cpuonline because the MSRs are at zero after cpu reset and also during
>
> Are you sure that the MSRs are zero when the cpu goes offline and then
> online again? That's not a reset.

Thats right - I was removing this since at the first sched_in the new CLOSID 
would be updated anyways. I know this prevents from having a 0 CLOSid at the 
time all the hot plug code is run, but we already have run the __cpu_disable and 
all the hotplug code when going down on the last used CLOSid. (if the kernel 
thread that handles the offline/online should have a 0 CLOS then thats fine 
probably..)
So may be the right way is to actually zero the CLOS in PQR_MSR when we are 
going down/offline ?

Thanks,
Vikas

>
> Thanks,
>
> 	tglx
>