On 20/06/2019 17:27, Andre Przywara wrote:
On Thu, 30 May 2019 15:15:12 +0100 Vincenzo Frascino vincenzo.frascino@arm.com wrote:
Hi,
vDSO (virtual dynamic shared object) is a mechanism that the Linux kernel provides as an alternative to system calls to reduce where possible the costs in terms of cycles. [ ... ] The porting has been benchmarked and the performance results are provided as part of this cover letter.
I can't reveal the absolute numbers here, but vdsotest-bench gives me quite some performance gain on my board here ("time needed on v6" divided by "time needed on 5.2-rc1", so smaller percentages are better): clock-gettime-monotonic: 23 % clock-gettime-monotonic-raw: 30 % clock-gettime-tai: 5 % clock-getres-tai: 5 % clock-gettime-boottime: 5 % clock-getres-boottime: 5 % clock-gettime-realtime: 25 % gettimeofday: 26 % The other numbers stayed the same or differed by just 1 ns, which seems to be within the margin of error, as repeated runs on the same kernel suggest. The 5% numbers are of course those were we went from a syscall-only to the newly added arm64 VDSO implementation, but even the other calls improved by a factor of 3 or more.
Sounds like a strong indicator that this is a good thing to have.
Not sure if "running some benchmark a couple of times on a single machine" qualifies for this, but I guess it means:
Tested-by: Andre Przywara andre.przywara@arm.com
Thanks Andre, it sounds great! I will add your tag as well to my patches.
Cheers, Andre.