Phoronix Benchmarks: Waht's wrong with FreeBSD 8.0?
se at freebsd.org
Mon Nov 30 17:52:32 UTC 2009
Am 30.11.2009 15:46, schrieb Ivan Voras:
> Robert Huff wrote:
>> Bill Moran writes:
>>> It's common knowledge that the default value for vfs.read_max is
>>> non- optimal for most hardware and that significant performance
>>> improvements can be made in most cases by raising it.
>> Documentation/discussion where?
> There is no documentation except for the sysctl documentation itself:
> "vfs.read_max: Cluster read-ahead max block count" but it depends on the
> load - it helps sequential reads, will probably do nothing for other
> kinds of loads. It is also UFS-only.
I tested different values some time ago. vfs.read_max can be raised to
about twice its default value and I set it to 15, when I had UFS+SU
file systems (switched over to ZFS, long ago.) Tests included operations
on large files (multi-GB) that were processed and written back to the
same drive. But even in these tests, there was an upper limit beyond
that system responsiveness declined massively (IIRC, at about 25). The
best value (without impact on randoim I/O) seems to be in the range
12 to 16. (FreeBSD used to apply a heuristic on read-ahead, and only
incremented the read amount to the limit set by the sysctl as long as
the accesses were purely sequential.)
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