3 ms·
There's some odd stuff: <<< PDEP/PEXT Parallel Bits Deposit/Extreact 300 cycle latency 250 per clock 3 cycle latency 1 per clock It’s worth highlighting t
by throwaway_pdp09 6y ago
There's some odd stuff:
<<<
PDEP/PEXT Parallel Bits
Deposit/Extreact 300 cycle latency
250 per clock 3 cycle latency
1 per clock
It’s worth highlighting those last two commands. Software that helps the prefetchers, due to how AMD has arranged the branch predictors, can now process three prefetch commands per cycle. The other element is the introduction of a hardware accelerator with parallel bits: latency is reduced 99% and throughput is up 250x.
>>>
It talks about pdep/pext and links them to prefetchers - what? Weirder yet "is the introduction of a hardware accelerator with parallel bits" all that's happened, and backed up by earlier info in the article, is that these were trapped+emulated before, hence their hideous cost, and now they're in hardware[0]. It comes across as if someone didn't understand that.
[0] calling it a 'hardware accelerator' is just peculiar.
- deleted 6y ago[deleted]
- wtallis 6y agoThe paragraph you quoted is referring to the last two rows of the preceding table, of which you've only quoted the last row.
- throwaway_pdp09 6y agoThe last two commands (their words) were PDEP/PEXT, but yeah, ISWYM. The description is still weird, and I notice in a preceding row "ANDN - Logical AND". I mean, would anyone technical have made that mistake?
- account42 6y agoThey weren't "trapped" but just implemented using complex/looping microcode whereas now they have dedicated hardware. The purpose of that hardware is to accelerate those operations.