Re: [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation.

[Christophe Leroy]

Hi

On 01/17/2020 08:58 AM, Segher Boessenkool wrote:
> Hi!
>
> On Thu, Jan 16, 2020 at 05:58:24PM +0000, Christophe Leroy wrote:
> > On a powerpc8xx, with current powerpc/32 ASM VDSO:
> >
> > gettimeofday:    vdso: 907 nsec/call
> > clock-getres-realtime:    vdso: 484 nsec/call
> > clock-gettime-realtime:    vdso: 899 nsec/call
> >
> > The first patch adds VDSO generic C support without any changes to common code.
> > Performance is as follows:
> >
> > gettimeofday:    vdso: 1211 nsec/call
> > clock-getres-realtime:    vdso: 722 nsec/call
> > clock-gettime-realtime:    vdso: 1216 nsec/call
> >
> > Then a few changes in the common code have allowed performance improvement. At
> > the end of the series we have:
> >
> > gettimeofday:    vdso: 974 nsec/call
> > clock-getres-realtime:    vdso: 545 nsec/call
> > clock-gettime-realtime:    vdso: 941 nsec/call
> >
> > The final result is rather close to pure ASM VDSO:
> > * 7% more on gettimeofday (9 cycles)
> > * 5% more on clock-gettime-realtime (6 cycles)
> > * 12% more on clock-getres-realtime (8 cycles)
>
> Nice!  Much better.
>
> It should be tested on more representative hardware, too, but this looks
> promising alright :-)

mpc832x (e300c2 core) at 333 MHz:

Before:

gettimeofday:    vdso: 235 nsec/call
clock-getres-realtime-coarse:    vdso: 1668 nsec/call
clock-gettime-realtime-coarse:    vdso: 1338 nsec/call
clock-getres-realtime:    vdso: 135 nsec/call
clock-gettime-realtime:    vdso: 244 nsec/call
clock-getres-boottime:    vdso: 1232 nsec/call
clock-gettime-boottime:    vdso: 1935 nsec/call
clock-getres-tai:    vdso: 1257 nsec/call
clock-gettime-tai:    vdso: 1898 nsec/call
clock-getres-monotonic-raw:    vdso: 1229 nsec/call
clock-gettime-monotonic-raw:    vdso: 1541 nsec/call
clock-getres-monotonic-coarse:    vdso: 1699 nsec/call
clock-gettime-monotonic-coarse:    vdso: 1477 nsec/call
clock-getres-monotonic:    vdso: 135 nsec/call
clock-gettime-monotonic:    vdso: 283 nsec/call

With the series:

gettimeofday:    vdso: 271 nsec/call
clock-getres-realtime-coarse:    vdso: 159 nsec/call
clock-gettime-realtime-coarse:    vdso: 184 nsec/call
clock-getres-realtime:    vdso: 163 nsec/call
clock-gettime-realtime:    vdso: 281 nsec/call
clock-getres-boottime:    vdso: 169 nsec/call
clock-gettime-boottime:    vdso: 274 nsec/call
clock-getres-tai:    vdso: 163 nsec/call
clock-gettime-tai:    vdso: 277 nsec/call
clock-getres-monotonic-raw:    vdso: 166 nsec/call
clock-gettime-monotonic-raw:    vdso: 302 nsec/call
clock-getres-monotonic-coarse:    vdso: 159 nsec/call
clock-gettime-monotonic-coarse:    vdso: 184 nsec/call
clock-getres-monotonic:    vdso: 166 nsec/call
clock-gettime-monotonic:    vdso: 274 nsec/call

Christophe