[1568] in linux-scsi channel archive
setting 2940 PCI burst length
daemon@ATHENA.MIT.EDU (Edward Welbon)
Wed Mar 19 05:24:54 1997
Date: Wed, 19 Mar 1997 03:46:53 -0600 (CST)
From: Edward Welbon <welbon@bga.com>
To: linux-scsi@vger.rutgers.edu
In-Reply-To: <Pine.LNX.3.91.970318213146.379A-100000@chaos.analogic.com>
I don't think that this is an adaptec or even a scsi question
specifically, anyway...
Can one set the burst length used by the 2940 in some way? I can set the
the global PCI latency via the bios menus of my P6DOF, (the setting is
reported back by the 2940 driver at boot) but I can't cahnge the burst
length via the bios menus. The driver declares the burst length to be "8
DWD" which I assume means 8 double words or 64 bytes (if a word is 8
bytes). Can I set this and if so, how?
Changing the PCI latency from 32 to 128 made a 25% improvement in
sequential read and seemed to make monitor and video card behave *much*
better (various retrace oddities vanished at max screen resolutions).
I understand that the PCI latency is a time in PCI clocks that a device is
allowed to hold ownership of the bus. If so, 128 cycles to move 64 bytes
seems leasurely. I speculate that I could have achieved the disk IO
performance improvement at 96 and even 64 PCI latency settings (didn't yet
try). So I wondered what might happen if I could increase the number of
bytes moved per burst to say 128 bytes with 128 (or larger) cycles for PCI
latency. Disk drives usually like to move data in long bursts.
Ed Welbon; welbon@bga.com;
Any sufficiently advanced technology is indistinguishable from linux...
Flush bill, choose linux.
