Re: diskio low read performance

On Sat, Jan 13, 2007 at 05:23:39PM -0200, Michel Santos wrote:

kernel config
http://suporte.lucenet.com.br/ms/kernel62

options SCHED_ULE # ULE scheduler

From the NOTES file from where you copied this:

# SCHED_ULE is a new scheduler that has been designed for SMP and has some
# advantages for UP as well. It is intended to replace the 4BSD scheduler
# over time. NOTE: SCHED_ULE is currently considered experimental and is
# not recommended for production use at this time.

When investigating problems with your system, your very first step
should be to revert the use of code marked "experimental" and "not
recommended for production use" ;-)


I am running both (on at a time of course :) ), now for six month or so,
ULE is giving me better overall performance, either with or w/o polling. I
mean network performance. I have net.isr.enable=1 and
net.inet.ip.fastforwarding=1,
this way I do get the same network performance I had on the 4.11. I mean I
have no problem here.

But also I checked the ULE/BSD against my particular problem and there is
no difference at all. I get no acceptable disk read performance when
comparing what I had with 4.11, wether with ULE or with 4BSD

Be very careful, because I've personally measured severe disk I/O
penalties with ULE on SMP hardware. In fact in my testing ULE gives
worse SMP performance under load across the board compared to 4BSD
(it's only faster for the lightest of workloads).

If you're absolutely certain that ULE is not to blame (and want to
continue to take the risk of other performance and stability problems
down the line), that basically leaves something to do with the scsi
driver and/or its interaction with your hardware as the probable
cause. I don't know enough about this particular hardware to comment
further though.

Some other comments about your config that are not likely to be
relevant for your I/O problem:

* it's not recommended to use an explicit maxusers value unless you
know that you need it; modern versions of FreeBSD auto-tune with
maxusers 0 which is the recommended configuration.

* adaptive mutexes are usually a win so it's a bit unusual that you
have disabled them, but I assume you have tested this.

* Dunno about the AUTO_EOI_1 option, I don't think you even have this
hardware on your system (device atpic didn't probe in your dmesg).

* HZ=1000 is superfluous since it is the default but may or may not
help. In some workloads the increased overhead relative to the old
default of HZ=100 gives a performance loss. Maybe it helps with
polling though, I dunno.

Kris

Attachment: pgpDZuQcQLlyv.pgp
Description: PGP signature

Relevant Pages

  • Re: Scheduler selection for web hosting
    ... 4BSD - which, AFAIK, is a renamed new SMP scheduler, but i'm not sure ... want to get max perfomance from it for web hosting. ... ULE is a new scheduler designed to take SMP into account. ...
    (freebsd-current)
  • Re: diskio low read performance
    ... penalties with ULE on SMP hardware. ... adaptec driver first, but even with the adaptec disabled and the LSI card ... I get better network performance when not using polling with it and seems ...
    (freebsd-performance)
  • Re: em driver input errors
    ... ULE or 4BSD ... Have you NIC IRQ sharing with other hardware? ... host# sysctl kern.sched.name kern.hz ... I don't use polling on FBSD 7.x, ...
    (freebsd-net)
  • Re: My wish list for 6.1
    ... >>> SMP versus UP on a socket 939 Opteron. ... >> If those results are accurate, there's no real reason not to just use an SMP ... > differ a lot across hardware variations. ... On modern Xeon P4 ...
    (freebsd-hackers)
  • RE: Anybody Use 2 or More CPU at Production Env. ( SMP )
    ... Anybody Use 2 or More CPU at Production Env. ... It could be your hardware, you need to debug your kernel. ... works just fine under any load. ... >somebody when enable SMP support system start to reset itself or under high ...
    (freebsd-isp)