linux-kernel - Re: [PATCH] powerpc/powernv: Add kernel cmdline parameter to disable imc

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Message-Id: <87infmeonf.fsf@linux.vnet.ibm.com>
Date:   Wed, 11 Oct 2017 07:25:24 +1100
From:   Stewart Smith <stewart@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        maddy@...ux.vnet.ibm.com, hemant@...ux.vnet.ibm.com,
        anju@...ux.vnet.ibm.com
Subject: Re: [PATCH] powerpc/powernv: Add kernel cmdline parameter to disable imc

Michael Ellerman <mpe@...erman.id.au> writes:
> Anju T Sudhakar <anju@...ux.vnet.ibm.com> writes:
>
>> Add a kernel command line parameter option to disable In-Memory Collection
>> (IMC) counters and add documentation. This helps in debug.
>
> I'd really rather we didn't. Do we *really* need this?
>
> We don't have command line parameters to disable any of the other ~20
> PMUs, why is this one special?

You could also do the same thing by editing the device tree before
booting your kernel, we do have the facility to do that in petitboot.

A recent firmware patch: https://patchwork.ozlabs.org/patch/823249/
would fix the firmware implementation where the counters were already
running before the INIT/START calls, which are likely the cause of the
problems that this patch is trying to work around.

I propose we have the firmware do the right thing and nothing special in
kernel. i.e. not to merge this.

-- 
Stewart Smith
OPAL Architect, IBM.