From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
To: torvalds@linux-foundation.org
Cc: akpm@linux-foundation.org, axboe@kernel.dk,
darrick.wong@oracle.com, david@fromorbit.com,
dchinner@redhat.com, josef@toxicpanda.com,
kent.overstreet@gmail.com, linux-bcache@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
peterz@infradead.org, tj@kernel.org, viro@zeniv.linux.org.uk,
zach.brown@ni.com
Subject: Re: bcachefs status update (it's done cooking; let's get this sucker merged)
Date: Sat, 29 Jun 2019 17:39:24 +0100 [thread overview]
Message-ID: <CAPweEDxufL1SHCh2ao7600fF9+aciMhr2V_5vxQN6S8r=u2W4g@mail.gmail.com> (raw)
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.
next reply other threads:[~2019-06-29 17:23 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-29 16:39 Luke Kenneth Casson Leighton [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-06-10 19:14 bcachefs status update (it's done cooking; let's get this sucker merged) Kent Overstreet
2019-06-10 20:46 ` Linus Torvalds
2019-06-11 1:17 ` Kent Overstreet
2019-06-11 4:33 ` Dave Chinner
2019-06-12 16:21 ` Kent Overstreet
2019-06-12 23:02 ` Dave Chinner
2019-06-19 8:21 ` Jan Kara
2019-06-11 4:55 ` Linus Torvalds
2019-06-11 14:26 ` Matthew Wilcox
2019-06-11 4:10 ` Dave Chinner
2019-06-11 4:39 ` Linus Torvalds
2019-06-11 7:10 ` Dave Chinner
2019-06-12 2:07 ` Linus Torvalds
2019-07-03 5:59 ` Stefan K
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