SCSI Controler SCRU32 becomes realy slow on the latest kernels

SCSI Controler SCRU32 becomes realy slow on the latest kernels

[Hartmut Manz]

I am using here 2 machines with the ICP Vortex SCSI-Controler SCRU32 for some 
years now.

After switching one machine from Debian 3.1 (sarge, with Kernel 2.6.8) to the 
upcoming Debian 4.0 (etch with Kernel 2.6.17 or 2.6.18) I have noticed that 
my scsi-devices become very slow while there is also a dramatical increase in
the sys time needed for I/O operations.

The machine is a dual processor Xeon system (2 * 2.2 GHz) with 2 GB memory.
The used scsi drives are seagate R10k and R15k disks.

i.e.  reading 1 GB from the first SCSI drive takes about:
xen-1:/var/log# time dd if=/dev/sda bs=256k count=4000 of=/dev/null
4000+0 records in
4000+0 records out
1048576000 bytes (1.0 GB) copied, 55.3079 seconds, 19.0 MB/s

real    0m55.361s
user    0m0.368s
sys     0m49.107s

There are two strange things: 
   1. The transfer rate is only 19 MB/sec what is very low for this machine.
       The expected value would be at least 50 MB/sec.

   2. the system time is in the same range as the real time and thats
       realy annoying,  on the old kernel the system time for such an operatin
       was about 7 sec.

Thanks for any help

Hartmut

-- 
-----------------------------------------------------------------------------
Hartmut Manz                                      WWW:    http://www.intes.de
INTES GmbH                                        Phone:  +49-711-78499-29
Schulze-Delitzsch-Str. 16                         Fax:    +49-711-78499-10
D-70565 Stuttgart                                 E-mail: manz@intes.de
      Gott spricht: Ich lasse dich nicht fallen und verlasse dich nicht.
------------------------------------------------------  Josua 1, 5b ---------

Re: SCSI Controler SCRU32 becomes realy slow on the latest kernels

[Andrew Morton]

> On Thu, 7 Dec 2006 14:28:44 +0100 Hartmut Manz <manz@intes.de> wrote:
> I am using here 2 machines with the ICP Vortex SCSI-Controler SCRU32 for some 
> years now.
> 
> After switching one machine from Debian 3.1 (sarge, with Kernel 2.6.8) to the 
> upcoming Debian 4.0 (etch with Kernel 2.6.17 or 2.6.18) I have noticed that 
> my scsi-devices become very slow while there is also a dramatical increase in
> the sys time needed for I/O operations.
> 
> The machine is a dual processor Xeon system (2 * 2.2 GHz) with 2 GB memory.
> The used scsi drives are seagate R10k and R15k disks.
> 
> i.e.  reading 1 GB from the first SCSI drive takes about:
> xen-1:/var/log# time dd if=/dev/sda bs=256k count=4000 of=/dev/null
> 4000+0 records in
> 4000+0 records out
> 1048576000 bytes (1.0 GB) copied, 55.3079 seconds, 19.0 MB/s
> 
> real    0m55.361s
> user    0m0.368s
> sys     0m49.107s

ouch.

> There are two strange things: 
>    1. The transfer rate is only 19 MB/sec what is very low for this machine.
>        The expected value would be at least 50 MB/sec.
> 
>    2. the system time is in the same range as the real time and thats
>        realy annoying,  on the old kernel the system time for such an operatin
>        was about 7 sec.
> 

It would help a lot of we can determine where the kernel is spending all this
time.  Can you please generate a kernel profile?

Start a large IO operation then, while it is running, run

#!/bin/sh
sudo opcontrol --stop
sudo opcontrol --shutdown
sudo rm -rf /var/lib/oprofile
sudo opcontrol --vmlinux=/boot/vmlinux-$(uname -r)
sudo opcontrol --start-daemon
sudo opcontrol --start
sleep 10
sudo opcontrol --stop
sudo opcontrol --shutdown
sudo opreport -l /boot/vmlinux-$(uname -r) | head -50

(might need some adjustments for distro variation)

Thanks.