40% IDE performance regression going from FC3 to FC5 with same kernel

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I'll be filing a FC5 performance bug for this but would like an opinion
 from the IDE kernel people just in case this has already been seen...

I just upgraded my home K7-800, 512MB RAM box from FC3 to FC5
 and noticed a disk performance slowdown while copying files around.

System has two 160GB disks, a Samsung SP1604N 2MB cache and
 a Maxtor 6Y160P0 8MB cache; both disks appear to be almost 2x
 slower both on hdparm -t tests (17-19MB/s against 33/35 MB/s) and
 on dd tests, like this:

FC3
[[email protected] tmp]# time dd if=/dev/hda of=/dev/null skip=200 bs=1024k count=200
200+0 records in
200+0 records out

real    0m4.623s
user    0m0.004s
sys     0m1.308s

FC5
[[email protected] tmp]#  time dd if=/dev/hda of=/dev/null skip=200 bs=1024k count=200
200+0 records in
200+0 records out
209715200 bytes (210 MB) copied, 9.67808 seconds, 21.7 MB/s

real    0m9.683s
user    0m0.008s
sys     0m1.400s


The initial tests were my last FC3 self-compiled kernel (2.6.16-rc5-git8)
 vs FC5's 2.6.16-1.2080_FC5 kernel; so just to be sure, I copied over
 from my FC3 partition the 2.6.16-rc5-git8 kernel and its config file,
 and rebuilt it under FC5, with just a few differences for the new USB
 2.0 disk I added to a PCI controller I just put in, namely

[[email protected] linux-2.6.16-rc5-git8]# diff .config
/fc3/usr/src/linux-2.6.16-rc5-git8/.config
4c4
< # Fri Apr  7 03:58:23 2006
---
> # Mon Mar  6 22:49:32 2006
1110,1112c1110
< CONFIG_USB_EHCI_HCD=m
< CONFIG_USB_EHCI_SPLIT_ISO=y
< CONFIG_USB_EHCI_ROOT_HUB_TT=y
---
> # CONFIG_USB_EHCI_HCD is not set
1115c1113
< CONFIG_USB_UHCI_HCD=m
---
> CONFIG_USB_UHCI_HCD=y
1218d1215
< # CONFIG_USB_SISUSBVGA is not set

The result is unexpected - performance delta is still there. Concatenating
 output from hdparm -i /dev/hda and hdparm /dev/hda for the same kernel
 under FC3 and FC5, the only difference is

[[email protected] ~]# diff /tmp/hdparm.out.2616rc2git8-fc5
/tmp/hdparm.out.2616rc2git8
14c14
<  Drive conforms to: (null):  ATA/ATAPI-1 ATA/ATAPI-2 ATA/ATAPI-3
ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7
---
>  Drive conforms to: (null):
27c27
<  geometry     = 19457/255/63, sectors = 312581808, start = 0
---
>  geometry     = 19457/255/63, sectors = 160041885696, start = 0

I'll try now and rebuild a 2.6.16-rc5-git8 kernel under FC5 with the
 FC3 GCC and see whether that is responsible for the performance
 drop... of course if anyone has any idea about what's going on, I
 will be happy to try out stuff. Attaching hdparm output from the FC5
 2.6.16-rc5-git8 just to show that there is DMA etc. all configured fine.


Thanks in advance, ciao,

--alessandro

 "Dreamer ? Each one of us is a dreamer. We just push it down deep because
   we are repeatedly told that we are not allowed to dream in real life"
     (Reinhold Ziegler)

Attachment: hdparm.out.2616rc5git8-fc5
Description: Binary data


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