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Date:      Mon, 21 Jan 2013 20:15:47 +0530
From:      "Desai, Kashyap" <>
To:        "" <>
Cc:        "Kenneth D. Merry" <>, "" <>, "McConnell, Stephen" <>
Subject:   Max Queue depth of HBA limited to 256 ?
Message-ID:  <>

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I was trying to check few things on LSI controller, where we have more than=
 256 queue depth support.
I added default maxtags in scsi/scsi_xpt.c as below. (Because I don't want =
mattags to restrict any outstanding commands the LSI HBA.

        /* Default tagged queuing parameters for all devices */
          /*vendor*/"*", /*product*/"*", /*revision*/"*"
        /*quirks*/0, /*mintags*/2, /*maxtags*/1024      <--- Default maxtag=
s were 256. I increase it to 10234

LSI's SAS-HBA and MR-HBA can support more than 256 outstanding commands in =
Firmware.  But due to some reason, I am not able to pump more than 256 outs=
tanding commands to the HBA.

I used "rawio -p 256 /dev/da1" and more /dev/dax in loop. I have sysctl par=
ameter in Driver to display outstanding "FW commands". Max value for FW out=
standing only goes up to 256.

Also from some other mail thread Subject "mfi driver performance", I found =
that folks talk about tuning queue depth _but_ nobody discussed to increase=
 it beyond 256. Is there any limitation in FreeBSD ?

~ Kashyap

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