On Tue, Oct 08, 2013 at 12:51:18PM +0530, Anshuman Khandual wrote:

On 10/08/2013 09:51 AM, Michael Ellerman wrote:

quoted

On Mon, Oct 07, 2013 at 10:00:26AM +0530, Anshuman Khandual wrote:

quoted

Right now the `config_bhrb` PMU specific call happens after write_mmcr0
which actually enables the PMU for event counting and interrupt. So
there is a small window of time where the PMU and BHRB runs without the
required HW branch filter (if any) enabled in BHRB. This can cause some
of the branch samples to be collected through BHRB without any filter
being applied and hence affecting the correctness of the results. This
patch moves the BHRB config function call before enabling the interrupts.

Patch looks good.

But it reminds me I have an item in my TODO list:
 - "Why can't config_bhrb() be done in compute_mmcr()" ?

compute_mmcr() function deals with generic MMCR* configs for normal PMU
events. Even if BHRB config touches MMCRA register, it's configuration
does not interfere with the PMU config for general events. So its best
to keep them separate. 

I'm unconvinced. If they'd been together to begin with this bug never
would have happened.

And there's the added overhead of another indirect function call.

Besides, we can always look at these code consolidation
issues in future. 

The future is now.

But this patch solves a problem which is happening right now.

Sure, I'm not saying we shouldn't merge it as a fix. But I think we
should do the cleanup to move it into compute_mmcr() for 3.13.

cheers