On Mon, 9 Jan 2017 16:35:17 +0000 Mel Gorman <mgor...@techsingularity.net> wrote: > The following is results from a page allocator micro-benchmark. Only > order-0 is interesting as higher orders do not use the per-cpu allocator
Micro-benchmarked with [1] page_bench02: modprobe page_bench02 page_order=0 run_flags=$((2#010)) loops=$((10**8)); \ rmmod page_bench02 ; dmesg --notime | tail -n 4 Compared to baseline: 213 cycles(tsc) 53.417 ns - against this : 184 cycles(tsc) 46.056 ns - Saving : -29 cycles - Very close to expected 27 cycles saving [see below [2]] > Signed-off-by: Mel Gorman <mgor...@techsingularity.net> > Acked-by: Hillf Danton <hillf...@alibaba-inc.com> Acked-by: Jesper Dangaard Brouer <bro...@redhat.com> [1] https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm/bench - Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer [2] Expected saving comes from Mel removing a local_irq_{save,restore} and adding a preempt_{disable,enable} instead. Micro benchmarking via time_bench_sample[3], we get the cost of these operations: time_bench: Type:for_loop Per elem: 0 cycles(tsc) 0.232 ns (step:0) time_bench: Type:spin_lock_unlock Per elem: 33 cycles(tsc) 8.334 ns (step:0) time_bench: Type:spin_lock_unlock_irqsave Per elem: 62 cycles(tsc) 15.607 ns (step:0) time_bench: Type:irqsave_before_lock Per elem: 57 cycles(tsc) 14.344 ns (step:0) time_bench: Type:spin_lock_unlock_irq Per elem: 34 cycles(tsc) 8.560 ns (step:0) time_bench: Type:simple_irq_disable_before_lock Per elem: 37 cycles(tsc) 9.289 ns (step:0) time_bench: Type:local_BH_disable_enable Per elem: 19 cycles(tsc) 4.920 ns (step:0) time_bench: Type:local_IRQ_disable_enable Per elem: 7 cycles(tsc) 1.864 ns (step:0) time_bench: Type:local_irq_save_restore Per elem: 38 cycles(tsc) 9.665 ns (step:0) [Mel's patch removes a ^^^^^^^^^^^^^^^^] ^^^^^^^^^ expected saving - preempt cost time_bench: Type:preempt_disable_enable Per elem: 11 cycles(tsc) 2.794 ns (step:0) [adds a preempt ^^^^^^^^^^^^^^^^^^^^^^] ^^^^^^^^^ adds this cost time_bench: Type:funcion_call_cost Per elem: 6 cycles(tsc) 1.689 ns (step:0) time_bench: Type:func_ptr_call_cost Per elem: 11 cycles(tsc) 2.767 ns (step:0) time_bench: Type:page_alloc_put Per elem: 211 cycles(tsc) 52.803 ns (step:0) Thus, expected improvement is: 38-11 = 27 cycles. [3] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/time_bench_sample.c CPU used: Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz Config options of interest: CONFIG_NUMA=y CONFIG_DEBUG_LIST=n CONFIG_VM_EVENT_COUNTERS=y
