lkml.org 
[lkml]   [2019]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: bcachefs status update (it's done cooking; let's get this sucker merged)
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.

\
 
 \ /
  Last update: 2019-06-29 19:25    [W:0.046 / U:0.268 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site