[sane-devel] Gt-30000 and epkowa - Was Fwd: sanner still jogs - more buffering ?

Olaf Meeuwissen olaf.meeuwissen at avasys.jp
Wed Jun 8 01:11:42 UTC 2011

Please keep this on the mailing list.  That way it will get archived and
be searchable for everyone.

Pete Lancashire <pete at petelancashire.com> writes:

> Here's the logs and some more information

Your logs indicate that the epkowa backend is not limiting the size of
its internal buffer to 32kb, so that shouldn't be the issue.

If you want to make real, real sure, modify the epkowa backend source
code at the end of backend/channel-scsi.c to read

  static size_t
  channel_scsi_max_request_size (const channel *self)
    size_t max_request_size = sanei_scsi_max_request_size;
    if (getenv ("SANE_SG_BUFFERSIZE"))
        max_request_size = atoi (getenv ("SANE_SG_BUFFERSIZE"));
    return max_request_size;

and set the SANE_SG_BUFFERSIZE to, say, 1MB.

> I only got a chance to test a few things last night
> the log you requested is attached as scsi-debug.log, the other log
> file called just log is debug set at 4 and with SANE_SG_BUFFERSIZE set
> to 1048576 ( 1 meg), the size changed in the log file, but not to 1
> MB. I did not try making the SANE_SG_BUFFERSIZE bigger, ran out of
> time.
> Another non sane/epokwa issue is when I set
> /proc/scsi/sg/def_reserved_size to 1048576 anytime i run scanimage it
> resets back to 32768. Not sure what is going on there. I did not have
> time to try a smaller size.

No clues on that here either.

> On a side note I've got a ticket open with Epson, basically all the
> literature on the GT-30000 says that its SCSI interface supports
> SCSI-2 and SCSI-3.

The specs on www.epson.com say that "SCSI: Requires ASPI-compliant
compatible SCSI 2 or SCSI 3 PCI card and cable (not included)".  My
interpretation of that is that you can connect it to a SCSI-3 card and
it'll work, not that it'll necessarily work at SCSI-3 specifications,
let alone at the (theoretical) maximum band width.

> Going by the response from support, it is now confirmed the interface
> is SCSI-2 ONLY and that using the wide connector the maximum (raw my
> word) data rate is 20 MBytes per second, and thats a Megabyte being
> 1,000,000 bytes. SCSI-2 is based on a 10 Megahertz clock so the real
> raw rate for a wide port is 20,000,000 bytes per second. The scanner
> in color mode is suppose to do 0.79 milliseconds per line or 9.079
> seconds per page.

I only get to 8.058 seconds per page (and you did too, earlier).
17 inches at 600 dpi with 0.79ms per line.

> A full page at 600 dpi, color is 214,812,000 bytes, which is
> 23,662.921 bytes per seconds, the interface is a maximum of 20,000,000
> bytes per seconds.

For the record, you are referring to an 8-bit RGB scan of the maximum
available scan area (11.7x17 in^2), right.

I get 26,658,227 bytes per second (at 8.058 seconds per page and
23,660,315 at 9.079).  Assuming that . is a typo ;-) Seeing that the max
SCSI-3 throughput is 20MB/s, you can't do any better than 214,812,000
bytes at 20MB/s is 10.740 seconds per page in getting images to your
computer.  Since you observe jogging several times per page (what
size?), obviously, transfers are going a fair bit slower than the max.

In private mail you mentioned that total scan times at 600dpi was
between 16 and 20 seconds, with and without speed=yes and that the
scanner jogs three or four times with speed=yes.  That clearly indicates
that the scan is speed-limited by the image data transfer.  Based on
your timings you're getting between 10.7 and 13.4 MB/s, which is above
the maximum band width for Fast SCSI interfaces but well below that for
Fast-Wide SCSI and Ultra SCSI[1].

 [1] http://en.wikipedia.org/wiki/SCSI#Parallel_SCSI

> Not good, both from a technical standpoint but if this is the issue,
> well .. i really hope this is not an issue, since I recommended quite
> a few GT-30000's and well may have those that were bought returned.
> thanks for all the help so far !!

Sorry that this is of not much help.
Olaf Meeuwissen, LPIC-2           FLOSS Engineer -- AVASYS CORPORATION
FSF Associate Member #1962               Help support software freedom

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