[Gluster-devel] performance issues Manoj found in EC testing

[Pranith Kumar Karampuri]

hi Xavi,
          Meet Manoj from performance team Redhat. He has been testing EC
performance in his stretch clusters. He found some interesting things we
would like to share with you.

1) When we perform multiple streams of big file writes(12 parallel dds I
think) he found one thread to be always hot (99%CPU always). He was asking
me if fuse_reader thread does any extra processing in EC compared to
replicate. Initially I thought it would just lock and epoll threads will
perform the encoding but later realized that once we have the lock and
version details, next writes on the file would be encoded in the same
thread that comes to EC. write-behind could play a role and make the writes
come to EC in an epoll thread but we saw consistently there was just one
thread that is hot. Not multiple threads. We will be able to confirm this
in tomorrow's testing.

2) This is one more thing Raghavendra G found, that our current
implementation of epoll doesn't let other epoll threads pick messages from
a socket while one thread is processing one message from that socket. In
EC's case that can be encoding of the write/decoding read. This will not
let replies of operations on different files to be processed in parallel.
He thinks this can be fixed for 3.9.

Manoj will be raising a bug to gather all his findings. I just wanted to
introduce him and let you know the interesting things he is finding before
you see the bug :-).
-- 
Pranith
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