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<TITLE>sane-devel: Re: scsi command queuing</TITLE>
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<META NAME="Author" CONTENT="Henning Meier-Geinitz (hmg-ml@gmx.de)">
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<META NAME="Subject" CONTENT="Re: scsi command queuing">
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<H1>Re: scsi command queuing</H1>
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<!-- received="Wed Jun 28 12:16:19 2000" -->
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<!-- name="Henning Meier-Geinitz" -->
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<STRONG>From:</STRONG> Henning Meier-Geinitz (<A HREF="mailto:hmg-ml@gmx.de?Subject=Re:%20scsi%20command%20queuing&In-Reply-To=<20000628202400.C5299@hmg1.vortex.swb.de>"><EM>hmg-ml@gmx.de</EM></A>)<BR>
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<STRONG>Date:</STRONG> Wed Jun 28 2000 - 11:24:00 PDT
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<P>
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<LI><STRONG>Next message:</STRONG> <A HREF="0206.html">Jochen Eisinger: "bug in saned..."</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0204.html">Henning Meier-Geinitz: "Re: Test backends with 'scanimage -T'"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0201.html">Oliver Rauch: "scsi command queuing"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0207.html">Oliver Rauch: "Re: scsi command queuing"</A>
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<P>
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Hi,
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<BR>
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<P>On Wed, Jun 28, 2000 at 05:26:23PM +0200, Oliver Rauch wrote:
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<BR>
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<EM>> has someone experience with a sane backend and scsi command queueing?
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</EM><BR>
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<P>I have tried this some weeks ago without much success. To be exact: it is
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<BR>
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possible to send more than one scsi_req_enter before scsi_req_wait and there
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<BR>
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is no problem with this. But it isn't faster than waiting for each request
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<BR>
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and then sending the next. I haven't looked deeply into the code (and I
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<BR>
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don't understand much of SCSI) but the following lines looked suspicous:
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<BR>
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(in scsi_rq_wait())
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<BR>
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/* Now issue next command asap, if any. We can't do this
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<BR>
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earlier since the Linux kernel has space for just one big
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<BR>
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buffer. */
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<BR>
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issue (req->next);
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<BR>
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<P>So if I understand this correctly the scsi_req_enter only shedules the
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<BR>
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request and it will be sent to the driver whenever any pending request is
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<BR>
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finished. Maybe the "Linux can only use one big buffer" is history with the
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<BR>
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newer sg drivers?
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<BR>
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<P><EM>> Unfortunetly it does not speed up scanning large images. It really looks like
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</EM><BR>
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<EM>> the comunication via the scsi bus is not fast enough.
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</EM><BR>
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<P>Same here. I looked at the scanning times when the backend does nothing but
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<BR>
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getting data from the scanner and ignoring it. There was no big change in
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<BR>
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scanning time (about 5 %). With the original SCSI adapter the Mustek
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<BR>
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scanners are about twice as slow as with Windows despite large (4 MB) SCSI
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<BR>
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buffers and tweaking the Linux SCSI driver.
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<BR>
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<P>Bye,
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<BR>
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Henning
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<BR>
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<P><PRE>
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--
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Source code, list archive, and docs: <A HREF="http://www.mostang.com/sane/">http://www.mostang.com/sane/</A>
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To unsubscribe: echo unsubscribe sane-devel | mail <A HREF="mailto:majordomo@mostang.com?Subject=Re:%20scsi%20command%20queuing&In-Reply-To=<20000628202400.C5299@hmg1.vortex.swb.de>">majordomo@mostang.com</A>
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</PRE>
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<LI><STRONG>Next message:</STRONG> <A HREF="0206.html">Jochen Eisinger: "bug in saned..."</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0204.html">Henning Meier-Geinitz: "Re: Test backends with 'scanimage -T'"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0201.html">Oliver Rauch: "scsi command queuing"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0207.html">Oliver Rauch: "Re: scsi command queuing"</A>
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<EM>
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This archive was generated by <A HREF="http://www.hypermail.org/">hypermail 2b29</A>
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: <EM>Wed Jun 28 2000 - 12:18:49 PDT</EM>
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