RPi2 i/o blocking and SD card performance

[Gergely Imreh]

Hi,

I've been testing FreeBSD 11.0-CURRENT on a RaspberryPi2. I'm relatively
new to FreeBSD, and wondering if there's any advice for improving the
performance a bit.

First, it looks like there's a lot of i/o blocking behaviour going on. For
example running MediaWiki on the board, if I compile any ports, the site
itself is pretty much unusable (the PHP scripts time out even with 180s
timeouts). The strangest thing is that the CPU usage is not at 100% all the
way, can be that all 4 cores are ~99% idle, and still everything goes very
slow. Once the ports compilation or any other i/o-related task is finished,
it's snappy again.

Any idea why it could be to have such big latency/lag even though the CPU
is idle? Is there anything I could test?

Second, I've also tried profiling the SD card a bit. The very same card
(SanDisk 32GB), same RPi board once with a fresh install of FreeBSD and
once with a fresh install of ArchLinuxARM, running bonnie++ -s 2000 (the
results below)

The block write perfomance on ArchLinux is ~55% higher (14M/s vs 9M/s),
while rewrite and per char output is 4-5x larger. Block read is also ~70%
larger (25M/s vs 15M/s). This is without any tuning. Any idea why the
FreeBSD performance on the exact same hardware is so different, and whether
it can be improved? I guess these two questions are related.

FreeBSD:
version  1.97       ------Sequential Output------ --Sequential Input-
--Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec
%CP
rpi2          2000M    20  99  8924  14  2275   4    39  99 14873  14  33.9
  4
Latency               481ms    4407ms    8319ms     244ms     153ms
 226s
Version  1.97       ------Sequential Create------ --------Random
Create--------
rpi2                -Create-- --Read--- -Delete-- -Create-- --Read---
-Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec
%CP
                 16   660  25 10388 100  3483  99  1532  58 10702  99  3531
 99
Latency              2769ms     375us     754us    1967ms     253us
512us

ArchLinux:
Version  1.97       ------Sequential Output------ --Sequential Input-
--Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec
%CP
alarmpi       2000M   102  99 13901  10  8089   7   579  99 25264   8  30.6
  1
Latency               115ms    5843ms    6381ms   22745us   54383us
40338ms
Version  1.97       ------Sequential Create------ --------Random
Create--------
alarmpi             -Create-- --Read--- -Delete-- -Create-- --Read---
-Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec
%CP
                 16  4460  38 +++++ +++  6002  34  4137  34 +++++ +++  7440
 43
Latency              1391us    3885us    3757us    1068us     113us
 1261us


Cheers,
   Greg