slow disk performance in Xen0 FC5

> On Wed, 2006-05-31 at 23:07 -0700, Ashe Canvar wrote:
> 
>> For instance my avg data read rate ( tested using
hdparm -t /dev/hda)
>> is 55MB/s using the regular smp kernel but it falls
to 2.6MB/s when I
>> boot into dom0. No other domains are runnign at
this point. I have
>> looked for incrementing interrupts in ide0 , there
are none.
> 
> There were some important fixes to Xen's irq delivery
mechanism that
> have been added to FC5 since the 1.2080 kernel you are
running.  Could
> you please try updating to a newer kernel and seeing if
you can
> reproduce the problem?

Same problem here. Machine is dog slow whenever disk
accesses are 
required. Running yum takes ages. This is a dual-cpu 2.4Ghz
xeon w/ATA 
drive.

Running a stock FC5 kernel I get ~30MB/sec read or write
bandwidth. With 
xen kernel I get 3-7MB/s in dom0 and it varies a lot.
Typically I see 
the following in top (this was taken while running yum):

[rootmedusa1 ~]# top

top - 16:19:22 up 11 min,  2 users,  load average: 0.69,
1.63, 1.43
Tasks:  72 total,   1 running,  71 sleeping,   0 stopped,  
0 zombie
Cpu(s):  7.4% us,  1.5% sy,  0.0% ni, 16.9% id,  0.0% wa,
74.2% hi,  0.0% si
Mem:    262308k total,   142696k used,   119612k free,    
9072k buffers
Swap:  1052248k total,        0k used,  1052248k free,   
49168k cached

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+
 COMMAND 

  2748 root      15   0 52860  42m 5268 S 49.9 16.5  
0:48.33 yum 

  2778 root      17   0  2140 1004  808 R 10.2  0.4  
0:01.75 top 

   368 root      16   0     0    0    0 S  0.6  0.0  
0:04.00 kjournald

Note the high %hi!
At almost the same time:

[rootmedusa1 ~]# iostat -x 10
Linux 2.6.16-1.2122_FC5xen0 (medusa1)   06/11/2006

avg-cpu:  %user   %nice %system %iowait   %idle
            1.02    0.00   64.62    0.00   34.36

Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s   
rkB/s    wkB/s 
avgrq-sz avgqu-sz   await  svctm  %util
hda          0.00   3.68  0.00  0.72    0.00   35.17    
0.00    17.59 
   49.14     0.00    0.00   0.00   0.00

Almost no disk activity, but high system time. I'm pretty
sure it was 
not doing network I/O.

[rootmedusa1 ~]# dmesg | head
Linux version 2.6.16-1.2122_FC5xen0 
(bhcompilehs20-bc1-3.build.redhat.com) (gcc version 4.1.0
20060304 (Red 
Hat 4.1.0-3)) #1 SMP Sun May 21 15:34:43 EDT 2006
[rootmedusa1 ~]# dmesg | egrep ATA
hda: ST380011A, ATA DISK drive
[rootmedusa1 ~]# dmesg | egrep IDE
PCI: Ignoring BAR0-3 of IDE controller 0000:00:1f.1
Uniform Multi-Platform E-IDE driver Revision: 7.00alpha2
ICH3: IDE controller at PCI slot 0000:00:1f.1

Well, the bottom line is that the machine is not usable like
this. Grrr.
Thorsten

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