On 08/31/2017 02:40 PM, Josh Boyer wrote:
> In summary:
>
> - Is the added performance of the multilib builds for users worth the
> build cost and development slowdown caused by slow builds?
That is indeed a good question overall. If the answer is no, then all
of the above is irrelevant. If the answer is yes, which I suspect it
to be, then data showing that would be good to have.
Josh,
I like your suggestion of removing POWER6 and POWER7 optimized versions
in anticipation that we'll have POWER8 and POWER9 going forward, leaving
only 3 multilibs: (a) most compatible and (b) N and N-1 for new hardware.
It's a reasonable tradeoff.
Florian,
Are you able to take master and run the microbenchmark on each of POWER6,
POWER7, and POWER8, building twice, once with no special options, and
once again with the required '-mcpu=powerX -mtune=powerX' (and
--with-cpu=powerX in configure)?
Nobody at this point has provided any data if there are discernible
differences between the multilibs, but now with what we have in our
microbenchmark it would represent some kind of data.
I might argue that if the benchmark doesn't show any statistically
significant gains between a generic build and a -mcpu/-mtune build
that we go ahead with your suggestion to drop all of the except the
most compatible one. At that point our position is defensible.
--
Cheers,
Carlos.