On Tue, Oct 15, 2013 at 09:32:48AM +0200, Ingo Molnar wrote: > > * Neil Horman <nhor...@tuxdriver.com> wrote: > > > On Sat, Oct 12, 2013 at 07:21:24PM +0200, Ingo Molnar wrote: > > > > > > * Neil Horman <nhor...@tuxdriver.com> wrote: > > > > > > > Sébastien Dugué reported to me that devices implementing ipoib (which > > > > don't have checksum offload hardware were spending a significant amount > > > > of time computing checksums. We found that by splitting the checksum > > > > computation into two separate streams, each skipping successive > > > > elements > > > > of the buffer being summed, we could parallelize the checksum operation > > > > accros multiple alus. Since neither chain is dependent on the result > > > > of > > > > the other, we get a speedup in execution (on hardware that has multiple > > > > alu's available, which is almost ubiquitous on x86), and only a > > > > negligible decrease on hardware that has only a single alu (an extra > > > > addition is introduced). Since addition in commutative, the result is > > > > the same, only faster > > > > > > This patch should really come with measurement numbers: what performance > > > increase (and drop) did you get on what CPUs. > > > > > > Thanks, > > > > > > Ingo > > > > > > > > > So, early testing results today. I wrote a test module that, allocated > > a 4k buffer, initalized it with random data, and called csum_partial on > > it 100000 times, recording the time at the start and end of that loop. > > It would be nice to stick that testcase into tools/perf/bench/, see how we > are able to benchmark the kernel's mempcy and memset implementation there: > Sure, my module is a mess currently. But as soon as I investigate the use of ADCX/ADOX that Anvin suggested I'll see about integrating that Neil
> $ perf bench mem memcpy -r help > # Running 'mem/memcpy' benchmark: > Unknown routine:help > Available routines... > default ... Default memcpy() provided by glibc > x86-64-unrolled ... unrolled memcpy() in arch/x86/lib/memcpy_64.S > x86-64-movsq ... movsq-based memcpy() in arch/x86/lib/memcpy_64.S > x86-64-movsb ... movsb-based memcpy() in arch/x86/lib/memcpy_64.S > > In a similar fashion we could build the csum_partial() code as well and do > measurements. (We could change arch/x86/ code as well to make such > embedding/including easier, as long as it does not change performance.) > > Thanks, > > Ingo > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
