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<TITLE>sane-devel: Re: scsi command queuing</TITLE>
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<META NAME="Author" CONTENT="Oliver Rauch (oliver.rauch@Wolfsburg.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="Sat Jul 1 13:28:26 2000" -->
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<!-- sent="Sat, 01 Jul 2000 22:43:21 +0200" -->
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<!-- name="Oliver Rauch" -->
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<!-- email="oliver.rauch@Wolfsburg.DE" -->
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<!-- subject="Re: scsi command queuing" -->
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<!-- id="395E57E9.D80FA51D@wolfsburg.de" -->
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<!-- inreplyto="395D347B.1E05897C@interlog.com" -->
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<STRONG>From:</STRONG> Oliver Rauch (<A HREF="mailto:oliver.rauch@Wolfsburg.DE?Subject=Re:%20scsi%20command%20queuing&In-Reply-To=<395E57E9.D80FA51D@wolfsburg.de>"><EM>oliver.rauch@Wolfsburg.DE</EM></A>)<BR>
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<STRONG>Date:</STRONG> Sat Jul 01 2000 - 13:43:21 PDT
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0004.html">abel deuring: "Re: scsi command queuing"</A>
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<P>
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Douglas Gilbert wrote:
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<BR>
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<P><EM>>
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</EM><BR>
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<EM>> Some info on Linux sg buffer sizes. DMA (used by most but not the very low
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</EM><BR>
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<EM>> end SCSI adapters) requires continuous buffers. ["continuous" seen from the
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</EM><BR>
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<EM>> PCI/ISA bus.] Linux actively discourages drivers taking big continuous
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</EM><BR>
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<EM>> buffers. So sg takes 32 KB chunks (controlled by the SG_SCATTER_SZ define
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</EM><BR>
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<EM>> in sg.h) and builds a scatter gather list. The adapter dictates the maximum
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</EM><BR>
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<EM>> number of the scatter gather list elements which is further limited to
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</EM><BR>
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<EM>> 255 elements. So that makes the maximum size of sg's reserve buffer
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</EM><BR>
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<EM>> (or any single command) just under 8 Megabytes. You can double
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</EM><BR>
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<EM>> SG_SCATTER_SZ, rebuild sg and perhaps get that number up to just under
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</EM><BR>
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<EM>> 16 Megabytes.
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</EM><BR>
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<EM>>
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</EM><BR>
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<P>Hi Douglas,
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<BR>
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<P>how large may SG_SCATTER_SZ be made? Are there any limits?
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<BR>
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What side effects do happen if I increase it to e.g. 128KB ?
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<BR>
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<P>Bye
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<BR>
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Oliver
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<BR>
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<P><P><PRE>
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--
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Homepage: <A HREF="http://www.wolfsburg.de/~rauch">http://www.wolfsburg.de/~rauch</A>
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sane-umax: <A HREF="http://www.wolfsburg.de/~rauch/sane/sane-umax.html">http://www.wolfsburg.de/~rauch/sane/sane-umax.html</A>
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xsane: <A HREF="http://www.wolfsburg.de/~rauch/sane/sane-xsane.html">http://www.wolfsburg.de/~rauch/sane/sane-xsane.html</A>
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E-Mail: mailto:<A HREF="mailto:Oliver.Rauch@Wolfsburg.DE?Subject=Re:%20scsi%20command%20queuing&In-Reply-To=<395E57E9.D80FA51D@wolfsburg.de>">Oliver.Rauch@Wolfsburg.DE</A>
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<P><P><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:%20scsi%20command%20queuing&In-Reply-To=<395E57E9.D80FA51D@wolfsburg.de>">majordomo@mostang.com</A>
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</PRE>
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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>Sat Jul 01 2000 - 13:33:54 PDT</EM>
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