Re: [PATCHv2 1/2] arm64:vdso: Rewrite gettimeofday into C.

[Yury Norov]

On Wed, May 31, 2017 at 01:44:30PM +0100, Will Deacon wrote:
> Hi Andrew,
> 
> Thanks for posting this, but please try to cc the maintainers in future -- I
> almost missed it!
> 
> On Tue, May 30, 2017 at 05:34:19PM -0700, Andrew Pinski wrote:
> > This allows the compiler to optimize the divide by 1000.
> > And remove the other divide.
> > 
> > On ThunderX, gettimeofday improves by 32%.  On ThunderX 2,
> > gettimeofday improves by 18%.
> > 
> > Note I noticed a bug in the old implementation of __kernel_clock_getres;
> > it was checking only the lower 32bits of the pointer; this would work
> > for most cases but could fail in a few.
> > 
> > Changes from v1:
> > * Fixed bug in __kernel_clock_getres for checking the pointer argument.
> > * Fix comments to refer to functions in arm64.
> 
> I tested this patch on a few platforms I have access to and didn't see the
> perf regressions I saw when I looked at this in the past with an older
> toolchain (it was mostly about the same, with a couple of improvements).
> 
> So, in principle, I'm not opposed to moving this into C. However, we're
> currently close to a "vDSO-explosion" on arm64 with people wanting a compat
> variant and also an ILP32 variant.

Hi Will,

This is the patch for ilp32. It's based on v1 but should be OK for v2
too. If vdso rework will be upstreamed prior to ilp32 series, I'll
incorporate it in ilp32.

Yury