From: Denys Vlasenko
> Sent: 21 November 2018 13:44
...
> I also tested this while working for string ops code in musl.
>
> I think at least 128 bytes would be the minimum where "REP insn"
> are more efficient. In my testing, it's more like 256 bytes...
What happens for misaligned copies?
I had a feeling that the ERMS 'reb movsb' code used some kind
of barrel shifter in that case.
The other problem with the ERMS copy is that it gets used
for copy_to/from_io() - and the 'rep movsb' on uncached
locations has to do byte copies.
Byte reads on PCIe are really horrid.
David
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