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Re: cvs pserver performance

From: Brian Behlendorf
Subject: Re: cvs pserver performance
Date: Thu, 25 Jan 2001 10:19:28 -0800 (PST)

On Thu, 25 Jan 2001, Larry Jones wrote:
> A good alternative to the memory based filesystem is a disk based
> filesystem that supports soft updates (even better than a virtual memory
> based filesystem, not quite as good as a physical memory based
> filesystem but a much more efficient use of resources).  

In terms of speed, a soft-updates file system is much faster than a
regular one, but not faster than memory-based.  I had /tmp on a
soft-updates filesystem before moving it and seeing speed
improvements.  Not to mention, taking all those ops/sec out of your disk
access queue will help improve I/O for all the other processes.

Ah, now I see you distinguish between a "virtual memory based
filesystem" and "physical memory based file system".  On something like
FreeBSD, I don't know that it makes much difference.  For what it's worth,
here's what I used to create the /tmp dir on FreeBSD 4.2 (inserted into
/etc/rc.local so it's there at startup)

  vnconfig -e -s labels,reserve -S 200m vn0
  disklabel -r -w vn0 auto
  newfs -i 1024 /dev/vn0c
  mount -o noatime /dev/vn0c /tmp
  chmod a+w /tmp
  chmod +t /tmp

This has the *positive* attribute of starting out with a clean /tmp on
reboot every time =)  It does mean that 200MB of swap is considered
allocated.  The "noatime" option avoids one op per access, updating the
last-access time.

One last optimization I was recommended and appeared to help: using sysctl
to set vfs.vmiodirenable=1.  Don't ask me to explain it.  =)


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