On Fri, 2017-09-01 at 09:24 -0500, Carlos O'Donell wrote:
On 09/01/2017 09:03 AM, Steven Munroe wrote:
> If you want to cut back you can't try 970 as base, plus power6 and
> power7 -mtune power8
s/can't/can/g?
I assume you're suggestion:
* 970 base multilib.
* power6 multilib.
* power7 multilib with power8 tunning.
Which implies:
* Drop the power8 multilib.
That drops only 1 multilib.
Do we need power6 or can we fold that into the 970?
e.g.
* 970 base multilib with power6 tuning.
* power7 multilib with power8 tuning.
That seems simple but is ignoring the major features added with each ISA
level.
So between 970 and power8 we added DFP, VSX, VSX Scalar Float, and HTM.
This is over 300 new instructions including additions to existing ISA
categories, like Fixed Point 64-bit, Floating Point, and VMX (Altivec)
beyond what was in 970.
So what you propose will mean Power6 would be restricted to software
emulation of DFP and the DFP hardware unused. And will not have the
mutex lock hint and compare bytes optimization.
Power7 will get both HW DFP and VSX (vector double and extended scalar
double) but without Scalar extended Float. Also will leave the HTM and
direct moves (GPR <-> VSR) optimization disabled.
So if you holding on to your Apple G5 you may not know what your
missing, but your P6 JS21 blade will be disappointing. And your P8 will
run slow due to missing direct move support.