On Mon, Jan 25, 2016 at 10:37:44AM -0800, Andy Lutomirski wrote: > On my Skylake laptop, INVPCID function 2 (flush absolutely > everything) takes about 376ns, whereas saving flags, twiddling > CR4.PGE to flush global mappings, and restoring flags takes about > 539ns.
FWIW, I ran your microbenchmark on the IVB laptop I have here 3 times and some of the numbers from each run are pretty unstable. Not that it means a whole lot - the thing doesn't have INVPCID support. I'm just questioning the microbenchmark and whether we should be rather doing those measurements with a real benchmark, whatever that means. My limited experience says that measuring TLB performance is hard. ./context_switch_latency 0 thread same use_xstate = 0 Using threads 1: 100000 iters at 2676.2 ns/switch 2: 100000 iters at 2700.2 ns/switch 3: 100000 iters at 2656.1 ns/switch ./context_switch_latency 0 thread different use_xstate = 0 Using threads 1: 100000 iters at 5174.8 ns/switch 2: 100000 iters at 5140.5 ns/switch 3: 100000 iters at 5292.9 ns/switch ./context_switch_latency 0 process same use_xstate = 0 Using a subprocess 1: 100000 iters at 2361.2 ns/switch 2: 100000 iters at 2332.2 ns/switch 3: 100000 iters at 3436.9 ns/switch ./context_switch_latency 0 process different use_xstate = 0 Using a subprocess 1: 100000 iters at 4713.6 ns/switch 2: 100000 iters at 4957.5 ns/switch 3: 100000 iters at 5012.2 ns/switch ./context_switch_latency 1 thread same use_xstate = 1 Using threads 1: 100000 iters at 2505.6 ns/switch 2: 100000 iters at 2483.1 ns/switch 3: 100000 iters at 2479.7 ns/switch ./context_switch_latency 1 thread different use_xstate = 1 Using threads 1: 100000 iters at 5245.9 ns/switch 2: 100000 iters at 5241.1 ns/switch 3: 100000 iters at 5220.3 ns/switch ./context_switch_latency 1 process same use_xstate = 1 Using a subprocess 1: 100000 iters at 2329.8 ns/switch 2: 100000 iters at 2350.2 ns/switch 3: 100000 iters at 2500.9 ns/switch ./context_switch_latency 1 process different use_xstate = 1 Using a subprocess 1: 100000 iters at 4970.7 ns/switch 2: 100000 iters at 5034.0 ns/switch 3: 100000 iters at 4991.6 ns/switch -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.