Re: [PATCH v3 21/26] arm64: Introduce asm/vdso/arch_timer.h

Will Deacon
2020-04-09T13:26:41Z

Hi Vincenzo,

Sorry, I was on holiday when you posted this and it slipped through the
cracks.

On Mon, Mar 16, 2020 at 03:37:23PM +0000, Vincenzo Frascino wrote:
> > On Fri, Mar 13, 2020 at 03:43:40PM +0000, Vincenzo Frascino wrote:
> >> The vDSO library should only include the necessary headers required for
> >> a userspace library (UAPI and a minimal set of kernel headers). To make
> >> this possible it is necessary to isolate from the kernel headers the
> >> common parts that are strictly necessary to build the library.
> >>
> >> Introduce asm/vdso/arch_timer.h to contain all the arm64 specific
> >> code. This allows to replace the second isb() in __arch_get_hw_counter()
> >> with a fake dependent stack read of the counter which improves the vdso
> >> library peformances of ~4.5%. Below the results of vdsotest [1] ran for
> >> 100 iterations.
> >
> > The subject seems to imply a non-functional change but as you read, it
> > gets a lot more complicated. Could you keep the functional change
> > separate from the header clean-up, maybe submit it as an independent
> > patch? And it shouldn't go in without Will's ack ;).
> >
>
> It is fine by me. I will repost the series with the required fixes and without
> this patch. This will give to me enough time to address Mark's comments as well
> and to Will to have a proper look.

Please can you post whatever is left at -rc1? I'll have a look then, but
let's stick to just moving code around rather than randomly changing it
at the same time, ok?

Thanks,

Will