LFS "smooth" syncer workaround/performance tuning

I'd grown annoyed at how LFS would blast data to the disk
according to
vfs.sync.*delay settings. A while ago, I thought, "why
not just
disable the sync delay altogether?"  Try setting:

vfs.sync.delay = 0
vfs.sync.filedelay = 0
vfs.sync.metadelay = 0
vfs.sync dirdelay = 0

Then, find out how much bandwidth you have at the inside and
outside
of your disk.  That is, run newfs_lfs -ANF on a partition
close to
cylinder 0, then do the same on a partition close to the
last
cylinder.  Average the two, then calculate the LFS
"page trip" with
the following formula (thanks tls):

t=(avg_bandwidth_in_bytes / PAGE_SIZE) / 4

I'd imagine that averaging is more or less moot if you don't
plan on
using > %50 of your disk's capacity, or if you are using
a partition
smaller than a majority of the disk.

Set vfs.lfs.pagetrip=t, and notice how data is now written
much more
smoothly to the disk.  You can fiddle with vfs.lfs.pagetrip
according
to the amount of latency you want.  This works especially
well with
BUFQ_PRIOCSCAN or BUFQ_READPRIO.  For further optimization,
I'd
recommend using BUFQ_PRIOCSCAN and tweaking the burst values
using
xtraeme's bufq sysctl patch:

http:
//www.xtrarom.org/patches/bufq_sysctl.diff

I'd be interested to hear if other people find this useful
or not.  I
find these settings useful enough such that I wish there
were a way to
turn off vfs sync only for LFS, as using these settings with
FFS isn't
too much fun. ;)


Regards,

--Blair


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"The frivolity and boredom which unsettle the
established order, the
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approaching change.  The gradual crumbling that left
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Hegel,
_Phenomenology of Spirit_ 5:11

This patch for bufq+sysctl is not optimal because it should
be using values 
per-drive
not globally, perhaps in the future I'll do it correctly...

----- Original Message ----- 
From: "Blair Sadewitz" <blair.sadewitzgmail.com>
To: <tech-performnetbsd.org>; <current-usersnetbsd.org>
Sent: Monday, April 02, 2007 3:15 AM
Subject: LFS "smooth" syncer
workaround/performance tuning


> I'd grown annoyed at how LFS would blast data to the
disk according to
> vfs.sync.*delay settings. A while ago, I thought,
"why not just
> disable the sync delay altogether?"  Try setting:
>
> vfs.sync.delay = 0
> vfs.sync.filedelay = 0
> vfs.sync.metadelay = 0
> vfs.sync dirdelay = 0
>
> Then, find out how much bandwidth you have at the
inside and outside
> of your disk.  That is, run newfs_lfs -ANF on a
partition close to
> cylinder 0, then do the same on a partition close to
the last
> cylinder.  Average the two, then calculate the LFS
"page trip" with
> the following formula (thanks tls):
>
> t=(avg_bandwidth_in_bytes / PAGE_SIZE) / 4
>
> I'd imagine that averaging is more or less moot if you
don't plan on
> using > %50 of your disk's capacity, or if you are
using a partition
> smaller than a majority of the disk.
>
> Set vfs.lfs.pagetrip=t, and notice how data is now
written much more
> smoothly to the disk.  You can fiddle with
vfs.lfs.pagetrip according
> to the amount of latency you want.  This works
especially well with
> BUFQ_PRIOCSCAN or BUFQ_READPRIO.  For further
optimization, I'd
> recommend using BUFQ_PRIOCSCAN and tweaking the burst
values using
> xtraeme's bufq sysctl patch:
>
> http:
//www.xtrarom.org/patches/bufq_sysctl.diff
>
> I'd be interested to hear if other people find this
useful or not.  I
> find these settings useful enough such that I wish
there were a way to
> turn off vfs sync only for LFS, as using these settings
with FFS isn't
> too much fun. ;)

It helps me out sufficiently, as I'm using an LFS ccd on
three
identical drives. ;)

--Blair

-- 
Support WFMU-FM: free-form radio for the masses!
<http://www.wfmu.org/>


"The frivolity and boredom which unsettle the
established order, the
vague foreboding of something unknown, these are the heralds
of
approaching change.  The gradual crumbling that left
unaltered the
face of the whole is cut short by a sunburst which, in one
flash,
illuminates the features of the new world."  --G.W.F.
Hegel,
_Phenomenology of Spirit_ 5:11