linux-kernel - Re: [RFC PATCH] arm64: topology: Map PPTT node offset to logic physical package id

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Date:   Thu, 28 Jun 2018 16:51:25 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Jeremy Linton <jeremy.linton@....com>,
        Shunyong Yang <shunyong.yang@...-semitech.com>,
        catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org,
        Joey Zheng <yu.zheng@...-semitech.com>
Subject: Re: [RFC PATCH] arm64: topology: Map PPTT node offset to logic
 physical package id

On Thu, Jun 28, 2018 at 03:09:19PM +0100, Sudeep Holla wrote:
> 
> 
> On 28/06/18 14:19, Jeremy Linton wrote:
> > Hi,
> > 
> > On 06/28/2018 07:12 AM, Sudeep Holla wrote:
> 
> [...]
> 
> >>
> >> OK sure. I liked the approach in Shunyong's patch. I was thinking if we
> >> can avoid the list and dynamic allocation on each addition and make it
> >> more simpler.
> >>
> > 
> > This one reads simpler, but yes I agree we should try to avoid the
> > dynamic allocation.
> > 
> > OTOH, I think that dropping the dynamic allocation leads to an algorithm
> > that picks a value and replaces all the matches. Which of course is
> > Andrew's patch, although I did have to read it a couple times to get a
> > grasp how it works. I'm guessing that is due to the fact that he seems
> > to have optimized 3 double loops into a single loop with two individual
> > nested loops. AKA its probably more efficient than the naive
> > implementation, but readability seems to have suffered a bit in the
> > initial version he posted. I'm not sure the optimization is worth it,
> > but I'm guessing there is a middle ground which makes it more readable.
> > 
> 
> Completely agree. RFC from Andrew is not so readable and easy to understand.

Middle ground coming up. At the expense of a triple-nested loop (which
will never be N^3 iterations due to conditions at the start of each loop),
we can avoid dynamic allocations and list iterations and still gain
readability.

Thanks,
drew