Re: "aborting sbp2 command" expected in kernel.org FireWire maybe

Mark Knecht wrote:
> The common answer around here is that:
>
> 1) The 2.4 series 1394 drivers work better than the 2.6 series drivers

Actually, the 1394 drivers combined with the Linux scsi subsystem and
other Linux facilities work more reliably in 2.4 than in 2.6. The
unreliablity of kernel 2.6 appears to be not solely related to the 1394
drivers. With respect to this, the 2.6 kernel line may be considered an
'odd numbered' line for the time being.

> 2) The 1394 drivers have never been optimized for performance

This is not completely true. There have been a few performance tweaks,
especially in the earlier history of the 1394 drivers.

But a *very* important optimization for throughput of asyncronous
transactions (such as used by sbp2 and eth1394) is the so-called gap
count optimization. This optimization is described in IEEE 1394a (and,
with mistakes, in 1394-1995). It shortens certain idle times of the bus.
Windows and apparently MacOS implement this optimization. Gap count
optimization is obsolete for pure 1394b buses.

According to
http://marc.theaimsgroup.com/?l=linux1394-devel&m=109128028930225 ,
raw async bandwith of an S400 bus is about 27 MByte/s without
optimization, and with gap count optimization on a short bus 44 MByte/s.
This sounds enormous, but consider that 1394 bus bandwith is not the
only limiting factor for real-life disk performance. On a reiserfs
formatted 5400 RPM drive I measured
  21 MByte/s write, 19 MByte/s read (sbp2 normal),
  25 MByte/s write, 24 MByte/s read (sbp2 + gap count optimization),
  32 MByte/s write, 30 MByte/s read (same disk on internal IDE),
for block-wise read/write operations on large files. Performance
differences for smaller files are much less pronounced. Of course, if a
very fast disk & bridge or more than one device is used at the same time
on a single S400 bus, the actual bus bandwith becomes more of a limiting
factor.

-- 
Stefan Richter
http://arcgraph.de/sr/
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