Re: Bad write performance with libata-tj-stable-2.6.17.4-20060710, pcmcia based sata_sil24, PMP, and NCQ drive

[Tejun Heo <htejun@gmail.com>]

Derek Taubert wrote:
> On Fri, Sep 01, 2006 at 10:34:59PM -0700, Derek Taubert wrote:
>> I'm now suspecting that the performance problems are due to bus issues
>> on the PCMCIA/PCI side.  Will poke around there and maybe try this with
>> a different laptop...
> 
> Found the problem!!!!

Great.

> The Cache Line Size field in the 3124 PCI Config Space needed to be
> set properly.  I suspect that this caused the 3124 DMA engine to issue
> non-burst reads for all data going toward the disk.  Since my old
> laptop has two bridges between host memory and the 3124, it surely made
> for some long read latencies (and thus very bad throughput).
> 
> Before:
> root@linux-srv:~ # od -Ax -t x4 /sys/bus/pci/devices/0000:06:00.0/config
> 000000 31241095 02b00087 01800001 00004000
> 000010 16008004 00000000 16000004 00000000
> 000020 00001c01 00000000 00000000 31241095
> 000030 00000000 00000064 00000000 0000010a
> 000040 00525407 12c3fff8 00000000 00000000
> 000050 00000000 00800005 00000000 00000000
> 000060 00000000 06224001 19002000 00000000
> 000070 00000000 00000000 00000000 00000000
> 
> I copied /sys/bus/pci/devices/0000:06:00.0/config to a temp file, used
> bvi to edit it, and then copied it back using dd:
> dd if=/tmp/sil24_config of=/sys/bus/pci/devices/0000:06:00.0/config bs=4 skip=3 seek=3 count=1 conv=notrunc
> 
> After:
> root@linux-srv:~ # od -Ax -t x4 /sys/bus/pci/devices/0000:06:00.0/config
> 000000 31241095 02b00087 01800001 00004008
> 000010 16008004 00000000 16000004 00000000
> 000020 00001c01 00000000 00000000 31241095
> 000030 00000000 00000064 00000000 0000010a
> 000040 00525407 12c3fff8 00000000 00000000
> 000050 00000000 00800005 00000000 00000000
> 000060 00000000 06224001 19002000 00000000
> 000070 00000000 00000000 00000000 00000000
> 
> root@linux-srv:~ # dd if=/dev/zero of=/dev/sda1 bs=1M count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 16.7798 seconds, 62.5 MB/s
> 
> Phew!  I was just about to spend a ridiculous amount of money on ebay for
> a logic analyzer...

How much was the price?

> I'm not sure if this will affect PCI-X configurations, but it is
> certainly worth trying.

Can you post full result of "lspci -vvv -xxx"?  I'm curious why things 
ended up that way.

Thanks.

-- 
tejun

-- 
VGER BF report: U 0.5