linux-kernel - Re: [PATCH v2] tools/power turbostat: Fix RAPL summary collection on AMD processors

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Date:   Tue, 20 Apr 2021 10:42:09 -0400
From:   Calvin Walton <calvin.walton@...stin.ca>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Borislav Petkov <bp@...e.de>, Terry Bowman <terry.bowman@....com>,
        lenb@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, wei.huang2@....com, aros@....com,
        rui.zhang@...el.com
Subject: Re: [PATCH v2] tools/power turbostat: Fix RAPL summary collection
 on AMD processors

On Tue, 2021-04-20 at 22:37 +0800, Chen Yu wrote:
> On Tue, Apr 20, 2021 at 09:28:06AM -0400, Calvin Walton wrote:
> > This patch has the same issue I noticed with the initial revision
> > of
> > Terry's patch - the idx_to_offset function returns type int (32-bit
> > signed), but MSR_PKG_ENERGY_STAT is greater than INT_MAX (or
> > rather,
> > would be interpreted as a negative number)
> > 
> > The end result is, as far as I can tell, that it hits the if
> > (offset <
> > 0) check in update_msr_sum() resulting in the timer callback for
> > updating the stat in the background when long durations are used to
> > not
> > happen.
> > 
> > For short durations it still works fine since the background update
> > isn't used.
> > 
> Ah, got it, nice catch. How about an incremental patch based on Bas'
> one
> to fix this 'overflow' issue? Would converting offset_to_idx(),
> idx_to_offset() and
> update_msr_sum() to use off_t instead of int be enough? Do you or
> Terry have interest
> to cook that patch? For Terry's version, I'm not sure if spliting
> the code into different CPU vendor would benefit in the future,
> except
> that we would have plenty of new MSRs to be introduced in the future.

Yes, I believe updating the offset_to_idx(), idx_to_offset(), and
update_msr_sum() functions is sufficient. I can do the incremental
patch for that this evening if nobody beats me to it :)

-- 
Calvin Walton <calvin.walton@...stin.ca>