Re: [PATCH] x86: skip delays during SMP initialization similar to Xen

Len Brown
2015-05-14T06:37:01Z

> [ 0.404369] x86: Booting SMP configuration:
...
> [ 2.737884] x86: Booted up 4 nodes, 120 CPUs
> [ 2.743758] smpboot: Total of 120 processors activated (671097.18 BogoMIPS)
>
> (2.743758-0.404369) = 2.339389 for all 119 processors
> /119 = .01965873109243697478 - lets call it 19ms each

For the record, the same (bare metal) box running latest tip boots
10ms/processor quicker
than upstream Linux, as expected. So this 120 processor box now
boots 1.19 seconds faster, in total.

[ 0.415969] x86: Booting SMP configuration:
...
[ 1.553658] x86: Booted up 4 nodes, 120 CPUs
[ 1.559173] smpboot: Total of 120 processors activated (671182.14 BogoMIPS)

1.553658-0.415969 = 1.137689 - seconds to bring 119 processors on-line.
./119 = .00956041176470588235 -- 9.5ms per processor, down from 19.

BTW. this time can be reduced by 7% (113 ms) by deleting announce_cpu():

[ 1.445815] x86: Booted up 4 nodes, 120 CPUs

cheers,
Len Brown, Intel Open Source Technology Center