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<TITLE>sane-devel: Re: Backend: When to use reader process?</TITLE>
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<META NAME="Author" CONTENT="Oliver Rauch (oliver.rauch@rauch-domain.de)">
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<META NAME="Subject" CONTENT="Re: Backend: When to use reader process?">
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<H1>Re: Backend: When to use reader process?</H1>
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<!-- received="Wed Feb 28 08:58:34 2001" -->
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<!-- name="Oliver Rauch" -->
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<!-- subject="Re: Backend: When to use reader process?" -->
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<STRONG>From:</STRONG> Oliver Rauch (<A HREF="mailto:oliver.rauch@rauch-domain.de?Subject=Re:%20Backend:%20When%20to%20use%20reader%20process?&In-Reply-To=<3A9D2CAF.6684A48B@rauch-domain.de>"><EM>oliver.rauch@rauch-domain.de</EM></A>)<BR>
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<STRONG>Date:</STRONG> Wed Feb 28 2001 - 08:51:59 PST
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<P>
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<LI><STRONG>Next message:</STRONG> <A HREF="0258.html">Henning Meier-Geinitz: "Re: preview and selectable scanarea for MFS-12000's ADF"</A>
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<UL>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0256.html">Oliver Rauch: "Re: xsane-win 0.72: netstart"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0253.html">Frederik Ramm: "Backend: When to use reader process?"</A>
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<HR NOSHADE><P>
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<P>
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Frederik Ramm wrote:
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<BR>
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<EM>>
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</EM><BR>
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<EM>> Hi,
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> I've noticed that the driver I am basing my M3091 work on, the
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</EM><BR>
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<EM>> M3096 driver which was in turn derived from the Coolscan driver, uses
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</EM><BR>
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<EM>> a separate process for reading data from the scanner, which is then
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</EM><BR>
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<EM>> fed via a pipe file descriptor to sane_read.
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> Other drivers (like the Bell+Howell backend I've been looking at for
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</EM><BR>
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<EM>> duplex inspiration) don't use a separate process.
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> Which would be the preferred way to implement it for a max. 15ppm ADF
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</EM><BR>
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<EM>> scanner?
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</EM><BR>
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<P>Hi Frederik,
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<BR>
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<P>the reader_process is a good and simple way to make sane_read
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<BR>
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independant from the scsi read commands.
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<BR>
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<P>When you do some tests you will notice that scanning speed
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<BR>
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on linux is limited to about 1MB/sec.
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<BR>
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<P>I did some tests to find out what causes that.
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<BR>
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The first guess was that the pipe slows down things so much
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<BR>
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and so I did some tests with mmaped transfers instead of
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<BR>
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the pipe. But that did not change anything.
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<BR>
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The speed limit to ca. 1MB/sec seems to be in the
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<BR>
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comunication between generic scsi (SG) <-> scsi driver <-> scsi hardware.
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<BR>
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<P>So as long as the speed is limited in the sg driver and kernel routines
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<BR>
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you do not get any problems with the reader process and pipe.
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<BR>
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(I did the test with an AMD K6-3/400Mhz). If I remeber right
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<BR>
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this is also valid for a Pentium 166.
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<BR>
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<P><P>Bye
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<BR>
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Oliver
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<BR>
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<P><PRE>
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--
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Homepage: <A HREF="http://www.rauch-domain.de">http://www.rauch-domain.de</A>
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sane-umax: <A HREF="http://www.rauch-domain.de/sane-umax">http://www.rauch-domain.de/sane-umax</A>
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xsane: <A HREF="http://www.xsane.org">http://www.xsane.org</A>
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E-Mail: mailto:<A HREF="mailto:Oliver.Rauch@rauch-domain.de?Subject=Re:%20Backend:%20When%20to%20use%20reader%20process?&In-Reply-To=<3A9D2CAF.6684A48B@rauch-domain.de>">Oliver.Rauch@rauch-domain.de</A>
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<P>--
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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:%20Backend:%20When%20to%20use%20reader%20process?&In-Reply-To=<3A9D2CAF.6684A48B@rauch-domain.de>">majordomo@mostang.com</A>
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</PRE>
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<!-- next="start" -->
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<LI><STRONG>Next message:</STRONG> <A HREF="0258.html">Henning Meier-Geinitz: "Re: preview and selectable scanarea for MFS-12000's ADF"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0256.html">Oliver Rauch: "Re: xsane-win 0.72: netstart"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0253.html">Frederik Ramm: "Backend: When to use reader process?"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0260.html">Uwe Wagner: "xsane crashes"</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 Feb 28 2001 - 09:00:45 PST</EM>
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