Hi, On Sat, Sep 26, 2020 at 3:27 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > Currently, we use the jiffies counter as a time source, by staring at > it until a HZ period elapses, and then staring at it again and perform > as many XOR operations as we can at the same time until another HZ > period elapses, so that we can calculate the throughput. This takes > longer than necessary, and depends on HZ, which is undesirable, since > HZ is system dependent. > > Let's use the ktime interface instead, and use it to time a fixed > number of XOR operations, which can be done much faster, and makes > the time spent depend on the performance level of the system itself, > which is much more reasonable. To ensure that we have the resolution > we need even on systems with 32 kHz time sources, while not spending too > much time in the benchmark on a slow CPU, let's switch to 3 attempts of > 800 repetitions each: that way, we will only misidentify algorithms that > perform within 10% of each other as the fastest if they are faster than > 10 GB/s to begin with, which is not expected to occur on systems with > such coarse clocks. > > On ThunderX2, I get the following results: > > Before: > > [72625.956765] xor: measuring software checksum speed > [72625.993104] 8regs : 10169.000 MB/sec > [72626.033099] 32regs : 12050.000 MB/sec > [72626.073095] arm64_neon: 11100.000 MB/sec > [72626.073097] xor: using function: 32regs (12050.000 MB/sec) > > After: > > [72599.650216] xor: measuring software checksum speed > [72599.651188] 8regs : 10491 MB/sec > [72599.652006] 32regs : 12345 MB/sec > [72599.652871] arm64_neon : 11402 MB/sec > [72599.652873] xor: using function: 32regs (12345 MB/sec) What are the chances of 12345 coming up? ;-) > > Link: https://lore.kernel.org/linux-crypto/20200923182230.22715-3-ardb@xxxxxxxxxx/ > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > crypto/xor.c | 38 +++++++++----------- > 1 file changed, 16 insertions(+), 22 deletions(-) This looks good to me. Thanks for taking this on! Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
