Re: [PATCH v5 0/5] Wire up getrandom() vDSO implementation on powerpc

[Christophe Leroy]

Le 04/09/2024 à 16:16, Jason A. Donenfeld a écrit :
> Hi Christophe, Michael,
>
> On Mon, Sep 02, 2024 at 09:17:17PM +0200, Christophe Leroy wrote:
> > This series wires up getrandom() vDSO implementation on powerpc.
> >
> > Tested on PPC32 on real hardware.
> > Tested on PPC64 (both BE and LE) on QEMU:
> >
> > Performance on powerpc 885:
> > 	~# ./vdso_test_getrandom bench-single
> > 	   vdso: 25000000 times in 62.938002291 seconds
> > 	   libc: 25000000 times in 535.581916866 seconds
> > 	syscall: 25000000 times in 531.525042806 seconds
> >
> > Performance on powerpc 8321:
> > 	~# ./vdso_test_getrandom bench-single
> > 	   vdso: 25000000 times in 16.899318858 seconds
> > 	   libc: 25000000 times in 131.050596522 seconds
> > 	syscall: 25000000 times in 129.794790389 seconds
> >
> > Performance on QEMU pseries:
> > 	~ # ./vdso_test_getrandom bench-single
> > 	   vdso: 25000000 times in 4.977777162 seconds
> > 	   libc: 25000000 times in 75.516749981 seconds
> > 	syscall: 25000000 times in 86.842242014 seconds
>
> Looking good. I have no remaining nits on this patchset; it looks good
> to me.
>
> A review from Michael would be nice though (in addition to the necessary
> "Ack" I need to commit this to my tree), because there are a lot of PPC
> particulars that I don't know enough about to review properly. For
> example, you use -ffixed-r30 on PPC64. I'm sure there's a good reason
> for this, but I don't know enough to assess it. And cvdso_call I have no
> idea what's going on. Etc.

You can learn a bit more about cvdso_call in commit ce7d8056e38b 
("powerpc/vdso: Prepare for switching VDSO to generic C implementation.")

About the fixed-r30, you can learn more in commit a88603f4b92e 
("powerpc/vdso: Don't use r30 to avoid breaking Go lang")


> But anyway, awesome work, and I look forward to the final stretches.

Thanks, looking forward to getting this series applied.

Christophe