Low performance of the IDE on the SIS550

[Yves Godin]

Hi everyone,
		I have a board based on the SIS550 (Vortex86 @167 MHz) and I wantd to 
setup a NFS file server that is capable to sustain 10 MBytes/s. But the 
problem is that the IDE interface seems very slow in writing. I patch my 
kernel (2.4.19) with the patch for the 5513 and now the controller is 
recognise as a ATA-100a but when I try to put the controller un UDMA mode 
mode 5, I got a message from hdparm that told that it is not supported.

Anyway, with the UDMA mode 2 I should have the performance that I need. I 
look on header of the ide connector and the burst when writing seems to be 
quick anough but between each of these bursts I have a hole of 5-6 seconds.

I test the speed with theses commands:

time dd if=/dev/zero of=zero bs=1k count=100k		-> WRITING
-> 30 sec

time dd if=zero of=/dev/null bs=1k count=100k		-> READING
-> 10 sec

I try all configuration possible (hdparm) for the harddisk and 3 MB/s is 
the best result that I got. In PIO mode 4, I only got a 1.5 MB/s !
I performed theses tests on different architecture and I got the following 
results:
	SC520		PIO (ISA)	->	 1.63 MB/s
	SC1210		PIO		->	 4.54 MB/s 	-> I was unable to enable the DMA ????
	P133		ATA-33		->	 5.50 MB/s
	PII-266		ATA-33		->	17.83 MB/s
	PII-400		ATA-33		->	20.54 MB/s
	C3-667		ATA-100	->	23.05 MB/s

Does anyone have an idea why:
	1. I cannot enable the UDMA mode 5 ?
	2. I only got 3 MBytes/s in writing ?



Thanks !

Yves