Messages in this thread | | | Date | Fri, 20 May 2022 17:55:05 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro |
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Hi Jens,
On Fri, May 20, 2022 at 09:44:25AM -0600, Jens Axboe wrote: > Ran 32, 1k, 4k here and it does seem to be down aboout 3%. Which is > definitely bigger than I expected, particularly for larger reads. If > anything, the 32b read seems comparably better than eg 1k or 4k, which > is also unexpected. Let me do a bit of profiling to see what is up.
Something to keep in mind wrt 32b is that for complicated crypto reasons, the function has this logic:
- If len <= 32, generate one 64 byte block and give <= 32 bytes of it to the caller.
- If len > 32, generate one 64 byte block, but give 0 of it to the caller. Then generate ⌈len/64⌉ blocks for the caller.
Put together, this means:
- 1..32, 1 block - 33..64, 2 blocks - 65..128, 3 blocks - 129..196, 4 blocks
So you get this sort of shelf where the amortization benefits don't really kick in until after 3 blocks.
> If you're worried about it, I'd just keep the read/write and add the > iter variants on the side. Not a chance of that. These functions are already finicky as-is; I would really hate to have to duplicate all of these paths.
Jason
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