Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] arm64: crypto: Add an option to assume NEON XOR is the fastest | Date | Tue, 22 Sep 2020 08:25:17 +0000 |
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From: Douglas Anderson > Sent: 22 September 2020 01:26 > > On every boot time we see messages like this: > > [ 0.025360] calling calibrate_xor_blocks+0x0/0x134 @ 1 > [ 0.025363] xor: measuring software checksum speed > [ 0.035351] 8regs : 3952.000 MB/sec > [ 0.045384] 32regs : 4860.000 MB/sec > [ 0.055418] arm64_neon: 5900.000 MB/sec > [ 0.055423] xor: using function: arm64_neon (5900.000 MB/sec) > [ 0.055433] initcall calibrate_xor_blocks+0x0/0x134 returned 0 after 29296 usecs > > As you can see, we spend 30 ms on every boot re-confirming that, yet > again, the arm64_neon implementation is the fastest way to do XOR. > ...and the above is on a system with HZ=1000. Due to the way the > testing happens, if we have HZ defined to something slower it'll take > much longer. HZ=100 means we spend 300 ms on every boot re-confirming > a fact that will be the same for every bootup.
Can't the code use a TSC (or similar high-res counter) to see how long it takes to process a short 'hot cache' block? That wouldn't take long at all.
David
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