Commit Graph

2 Commits

Author SHA1 Message Date
Jakob Unterwurzacher
9837cb0ddc cryptocore: prefetch nonces in the background
Spawn a worker goroutine that reads the next 512-byte block
while the current one is being drained.

This should help reduce waiting times when /dev/urandom is very
slow (like on Linux 3.16 kernels).
2017-06-11 21:29:50 +02:00
Jakob Unterwurzacher
80516ed335 cryptocore: prefetch nonces in 512-byte blocks
On my machine, reading 512-byte blocks from /dev/urandom
(same via getentropy syscall) is a lot faster in terms of
throughput:

Blocksize    Throughput
 16          28.18 MB/s
512          83.75 MB/s

For a single-threaded streaming write, this drops the CPU usage of
nonceGenerator.Get to almost 1/3:

        flat  flat%   sum%        cum   cum%
Before     0     0% 95.08%      0.35s  2.92%  github.com/rfjakob/gocryptfs/internal/cryptocore.(*nonceGenerator).Get
After  0.01s 0.092% 92.34%      0.13s  1.20%  github.com/rfjakob/gocryptfs/internal/cryptocore.(*nonceGenerator).Get

This change makes the nonce reading single-threaded, which may
hurt massively-parallel writes.
2017-06-09 22:05:14 +02:00