> -----Original Message----- > From: Brian Brooks [mailto:[email protected]] > Sent: Wednesday, April 19, 2017 9:37 PM > To: Savolainen, Petri (Nokia - FI/Espoo) <[email protected]> > Cc: Honnappa Nagarahalli <[email protected]>; lng- > [email protected] > Subject: Re: [lng-odp] [API-NEXT PATCH 8/8] linux-gen: time: use hw time > counter when available > > On 04/26 07:11:57, Savolainen, Petri (Nokia - FI/Espoo) wrote: > > > > > > > > From coverletter: > > > > "This patch set modifies time implementation to use TSC when running > on > > > a x86 > > > > CPU that has invarint TSC CPU flag set. Otherwise, the same Linux > system > > > time > > > > is used as before. TSC is much more efficient both in performance > and > > > > latency/jitter wise than Linux system call. This can be seen also > with > > > > scheduler latency test which time stamps events with this API. All > > > latency > > > > measurements (min, ave, max) improved significantly." > > > > > > odp_sched_latency currently uses clock_gettime. It is my understanding > > > that clock_gettime does not have the over head of the system call. Can > > > you elaborate more on the 'improved significantly' part? > > > > > > > clock_gettime() uses the same TSC, but when you profile it with perf you > can see tens of kernel functions including system call entry, RCU > maintenance, etc. > > > > E.g. in sched_latency test kernel consumed about 10% of all the cycles. > Also latency measurement results improved like this: > > * min >3x lower > > * avg 2x lower > > * max more stable and 50% lower > > You might want to share more information on the environment > where you're seeing such significant improvements because the > results on Broadwell do not match the above interpretation. > > PS - This patch series breaks the build on ARM. >
Use v2. It should build on ARM. -Petri
