Hi Sarosh, On Tue, Jul 28, 2020 at 06:30:46PM +0500, Sarosh Arif wrote: > Hello, > The following things made me think that rte_memcpy() is more optimized > than memcpy(): > 1. dpdk documentation recommends to use rte_memcpy() instead of memcpy(): > https://doc.dpdk.org/guides/prog_guide/writing_efficient_code.html > 2. Here some benchmarks are available: > > https://software.intel.com/content/www/us/en/develop/articles/performance-optimization-of-memcpy-in-dpdk.html > 3. rte_memcpy() has __attribute__((always_inline)) associated with it, > so compiler also tries to inline it. > > Using rte_memcpy() everywhere ensures consistency in code-base. > Here are the results of the performance number measurement using "perf": > > rte_memcpy() > > Performance counter stats > 1.573864 task-clock (msec) # 0.898 CPUs > utilized > 0 context-switches # 0.000 K/sec > 0 cpu-migrations # 0.000 K/sec > 342 page-faults # 0.217 M/sec > 5,483,016 cycles # 3.484 GHz > 5,554,017 instructions # 1.01 insn per > cycle > 1,114,593 branches # 708.189 M/sec > 33,796 branch-misses # 3.03% of all > branches > 1,369,247 L1-dcache-loads # 869.991 M/sec > <not counted> L1-dcache-load-misses > (0.00%) > <not counted> LLC-loads > (0.00%) > <not counted> LLC-load-misses > (0.00%) > > 0.001753373 seconds time elapsed > > > > memcpy() > > Performance counter stats > 1.631135 task-clock (msec) # 0.902 CPUs > utilized > 0 context-switches # 0.000 K/sec > 0 cpu-migrations # 0.000 K/sec > 342 page-faults # 0.210 M/sec > 5,676,549 cycles # 3.480 GHz > (73.99%) > 5,739,593 instructions # 1.01 insn per > cycle > 1,141,121 branches # 699.587 M/sec > 34,553 branch-misses # 3.03% of all > branches > 1,417,494 L1-dcache-loads # 869.023 M/sec > 67,312 L1-dcache-load-misses # 4.75% of all > L1-dcache hits (26.01%) > <not counted> LLC-loads > (0.00%) > <not counted> LLC-load-misses > (0.00%) > > 0.001808500 seconds time elapsed >
Can you give more details about your use-case? I mean what code are you running for this benchmark. I'll tend to agree with Stephen: memcpy() with a constant (small) size should directly be replaced by the optimal code for this architecture. rte_memcpy() uses vector instructions, and is probably better than libc's memcpy for larger copies. Thanks, Olivier > > > On Thu, Jul 23, 2020 at 8:47 PM Stephen Hemminger > <step...@networkplumber.org> wrote: > > > > On Thu, 23 Jul 2020 12:02:40 +0500 > > Sarosh Arif <sarosh.a...@emumba.com> wrote: > > > > > Since rte_memcpy is more optimized it should be used instead of memcpy > > > > > > Signed-off-by: Sarosh Arif <sarosh.a...@emumba.com> > > > > Really did you measure this. > > For fixed size structures, compiler can inline memcpy small set of > > instructions.
