# Re: scsi command queuing

From: Oliver Rauch (oliver.rauch@Wolfsburg.DE)
Date: Wed Jun 28 2000 - 15:22:23 PDT

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  Wolfgang Rapp wrote:

  >
  > But I think the most bottlenek is the interaktion between backends and kernel
  > after every scsi-command. This interaction time by
  > system calls , kernel scheduling etc. at this time is to long to keep the
  > scanner running, the next scan command block should be send
  > by the driver if it receives the completion interrupt from the last.

  Hi Wolfgang,

  if I do not send the image data from the reader_process to the main process
  (only send read commands to the scsi bus) the scanning speed is not increased.
  So I also think it is a problem between sanei_scsi, the sg driver and the kernel
  lowlevel scsi driver. In sanei_scsi there also is a not really necessary memcpy
  command but I do not think that this command does make the problem.

  A bit strange is that it does not make any differences if I use 32 KB or 256KB
  for the read command buffer (The scanner has 256KB internal image data).

  >
  > If we talk about scanspeed we should think about extending the sg driver for
  > doublebuffering data pages in kernel memory space
  > and command block repeat count. Filling one buffer by dma from scsi hardware
  > and coping in parallel the other out to the user
  > space instead of waiting for interrupts. My somebody have looked more to the
  > linux sg driver source code then I and knows more
  > about how it works.

  Hi Dough,
  any comments?!

  Bye
  Oliver

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