svn commit: r219699 - head/sys/kern

[Ivan Voras]

On 16 March 2011 18:46, Roman Divacky <rdivacky at freebsd.org> wrote:
>
> On Wed, Mar 16, 2011 at 04:22:59PM +0000, Ivan Voras wrote:
> > Author: ivoras
> > Date: Wed Mar 16 16:22:59 2011
> > New Revision: 219699
> > URL: http://svn.freebsd.org/changeset/base/219699
> >
> > Log:
> >   The hardware has caught up; improvements are now observed even at 128,
> >   but stay conservative and bump read_max to "only" 64 (it will probably be
> >   a good idea to increase this to 128 after the next major release).
>
> how did you measure this?

Specifically for this commit: my desktop 2xSATA 7200 RPM drives,
gmirror, single read "dd" stream, bs=1m. (Are there any ready read
multi-stream read tests which are not trivial i.e. they start from
different positions in the file?)

results:

read_max=32  -> 78 MB/s
read_max=64  -> 136 MB/s
read_max=128 -> 141 MB/s

I'm the one who previously bumped read_max from 8 to 32 about a year
ago, based on tests under an (otherwise idle, naturally) VMWare
cluster on a FC SAN, and a similar point of saturation was at
read_max=64. Now it is at 128 with raw hardware.

Maybe it should be tuned at 2^(major_freebsd_version-2)  :)

(as for safety & stability, I've put 2-3 new web servers in production
this year with read_max=128 irregardless of this commit. It's stable).