Re: Network very very slow... was iSCSI and jumbo frames

[mlelstv%serpens.de@localhost (Michael van Elst)]

joel.bertrand%systella.fr@localhost (=?UTF-8?Q?BERTRAND_Jo=c3=abl?=) writes:

>186 MB/s for the first file. 18,7 MB/s for the second one and about 10
>MB/s fort the third one.

When dd gets slow, check with 'top' for what condition the processes
wait. Example for writing with 'dd' to a FFSv2 32kB blocks, 4k frags
backed by an iSCSI disk.

  PID   LID USERNAME PRI STATE      TIME   WCPU    CPU NAME      COMMAND
    0   243 root     123 conn/2     0:05  5.96%  5.96% ConnSend  [system]
 3135  3135 mlelstv   85 pager_/0   0:02  3.28%  3.03% -         dd
    0   969 root     124 syncer/1  60:47  0.44%  0.44% ioflush   [system]
    0     9 root     125 vdrain/1   1:48  0.00%  0.00% vdrain    [system]
    0 17657 root     123 netio/1    0:01  0.00%  0.00% ConnRcv   [system]

In this state I get about 680Mbit/s between a wm0 (client) and re0 (server).
The iSCSI server is istgt on an Intel Atom running NetBSD-9. The performance
is mostly limited  by the server CPU.

ConnSend is waiting for something to do ("conn"), dd is waiting for I/O buffers ("pager_map"), ioflush waits for the syncer to flush the file cache ("syncer"),
vdrain is waiting for expunging vnodes when memory gets low ("vdrain") and ConnRecv is waiting for a response from the iSCSI server.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."