Messages in this thread | | | Date | Mon, 18 Dec 2023 01:41:33 +0000 | Subject | Re: [PATCH] riscv: lib: Optimize 'strlen' function | From | Ivan Orlov <> |
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On 12/17/23 17:00, David Laight wrote: > I'd also guess that pretty much all the calls in-kernel are short. > You might try counting as: histogram[ilog2(strlen_result)]++ > and seeing what it shows for some workload. > I bet you (a beer if I see you!) that you won't see many over 1k.
Hi David,
Here is the statistics for strlen result:
[ 223.169575] Calls count for 2^0: 6150 [ 223.173293] Calls count for 2^1: 184852 [ 223.177142] Calls count for 2^2: 313896 [ 223.180990] Calls count for 2^3: 185844 [ 223.184881] Calls count for 2^4: 87868 [ 223.188660] Calls count for 2^5: 9916 [ 223.192368] Calls count for 2^6: 1865 [ 223.196062] Calls count for 2^7: 0 [ 223.199483] Calls count for 2^8: 0 [ 223.202952] Calls count for 2^9: 0 ...
Looks like I've just lost a beer :)
Considering this statistics, I'd say implementing the word-oriented strlen is an overcomplication - we wouldn't get any performance gain and it just doesn't worth it.
I simplified your code a little bit, it looks like the alignment there is unnecessary: QEMU test shows the same performance independently from alignment. Tests on the board gave the same result (perhaps because the CPU on the board has 2 DDR channels?)
mv t0, a0 1: lbu t1, 0(a0) lbu t2, 1(a0) addi a0, a0, 2 beqz t1, 2f bnez t2, 1b addi a0, a0, 1 2: addi a0, a0, -2 sub a0, a0, t0 ret
If it looks good to you, would you mind if I send the patch with it? Could I add you to suggested-by tag?
-- Kind regards, Ivan Orlov
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