Messages in this thread | | | From | Luke Kenneth Casson Leighton <> | Date | Sat, 29 Jun 2019 17:39:24 +0100 | Subject | Re: bcachefs status update (it's done cooking; let's get this sucker merged) |
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hey linus, you made news again, all blown up and pointless again. you're doing great: you're being honest. remember the offer i made to put you in touch with my friend.
anecdotal story: andrew tridgell worked on the fujitsu sparc supercomputer a couple decades ago: it had a really weird DMA ring bus.
* memory-to-memory copy (in the same core) was 10mbytes/sec * DMA memory-to-memory copy (in the same core) was 20mbytes/sec * memory-memory copy (across the ring bus i.e. to another machine) was 100mbytes/sec * DMA memory-memory copy (across the ring bus) was *200* mbytes/sec.
when andrew tried asking people, "hey everyone, we need a filesystem that can work really well on this fast parallel system", he had to continuously fend off "i got a great idea for in-core memory-to-memory cacheing!!!!" suggestions, because they *just would never work*.
the point being: caches aren't always "fast".
/salutes.
l.
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