On Mon, 29 Jun 2009, Lejun Zhu wrote:
With ZFS write throttle, the number 2.5GB is tunable. From what I've
read in the code, it is possible to e.g. set
zfs:zfs_write_limit_override = 0x8000000 (bytes) to make it write
128M instead.
This works, and the difference in behavior is profound. Now it is a
matter of finding the "best" value which optimizes both usability and
performance. A tuning for 384 MB:
# echo zfs_write_limit_override/W0t402653184 | mdb -kw
zfs_write_limit_override: 0x30000000 = 0x18000000
CPU is smoothed out quite a lot and write latencies (as reported by a
zio_rw.d dtrace script) are radically different than before.
Perfmeter display for 256 MB:
http://www.simplesystems.org/users/bfriesen/zfs-discuss/perfmeter-256mb.png
Perfmeter display for 384 MB:
http://www.simplesystems.org/users/bfriesen/zfs-discuss/perfmeter-384mb.png
Perfmeter display for 768 MB:
http://www.simplesystems.org/users/bfriesen/zfs-discuss/perfmeter-768mb.png
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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