linux-kernel - Re: [PATCH 1/2] x86, sched: Prevent divisions by zero in frequency invariant accounting

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Date:   Tue, 19 May 2020 18:46:47 +0200
From:   Giovanni Gherdovich <ggherdovich@...e.cz>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...e.de>,
        Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86, sched: Prevent divisions by zero in frequency
 invariant accounting

On Mon, 2020-05-18 at 15:20 -0700, Ricardo Neri wrote:
> On Sat, May 02, 2020 at 04:25:00PM +0200, Giovanni Gherdovich wrote:
> > > 
> > > I've changed the patch like so.. OK?
> > > 
> > > (ok, perhaps I went a little overboard with the paranoia ;-)
> > 
> > Right, I wasn't really checking for overflow, only for when the product
> > "mcnt * arch_max_freq_ratio" becomes zero.
> > 
> > Thanks for your edit (I took note of the macros check_*_overflow, didn't know
> > them). I fully subscribe to the paranoid approach.
> > 
> > I understand you've already edited the patches in your tree, so I am not
> > resending, just confirming my
> > 
> > Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
> 
> Hi, have these changes been merged? I still don't see them in the tip or
> Linus' tree.
> 

Hi Ricardo,

the kbuild bot found an error in this patch, the macro check_mul_overflow
doesn't build on x86 32bit, so Peter Zijlstra hasn't merged it yet.
This is the error:
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/thread/7GDIBOMNVDG5W2XZD4EICE2TUZR3THBN/

I'm writing a patch to avoid doing frequency invariance entirely on i386.
I doubt those machines have APERFMPERF anyways. This will fix the build error.


Cheers,
Giovanni