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From: Bill Paul <wpaul@FreeBSD.ORG>
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	Fri, 21 Aug 1998 09:58:49 -0700 (PDT)
Date: Fri, 21 Aug 1998 09:58:49 -0700 (PDT)
Message-Id: <199808211658.JAA23928@freefall.freebsd.org>
To: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG
Subject: cvs commit: src/sys/pci if_xlreg.h
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wpaul       1998/08/21 09:58:49 PDT

  Modified files:
    sys/pci              if_xlreg.h 
  Log:
  Increase the number of descriptors (and, as a consequence, the number
  of associated mbuf clusters) in the RX ring from 4 to 16. On my
  really fast PI 400Mhz test machines, 4 descriptors (and associated
  mbuf clusters) is enough to achieve decent performance without any
  RX overruns. However, one person reported problems with the following
  scenario:
  
  - P90 system running FreeBSD with a 3c905B-TX adapter, slow IDE hard
    disk (Quantum Bigfoot?)
  - PII 266 with SCSI disks running LoseNT and also with a 3c905B-TX
  - Both machines connected together via crossover cable at 100Mbps
    full-duplex
  - LoseNT machine writing largs amounts of data (2.5 GB work of
    files each in the neighborhood of 1 to 2 MB in size) via samba to
    the FreeBSD machine
  
  In this case, the LoseNT machine is sending data very fast. Apparently
  there weren't any problems initially because the user was writing to
  one particular disk which was relatively fast, however after this disk
  filled up and the user started writing to the second slower disk, RX
  overruns would occur and sometimes the RX DMA engine would stall after
  a 100 to 500MB had been transfered. The xl_rxeof() handler is supposed
  to detect this condition and restart the upload engine; I'm not sure
  why it doesn't, unless interrupts are being lost and the rx handler
  isn't getting called.
  
  This is still an improvement over the Linux driver, which uses 32
  descriptors in its receive ring. :)
  
  Problem reported by: Heiko Schaefer <hschaefer@fto.de>
  
  Revision  Changes    Path
  1.2       +2 -2      src/sys/pci/if_xlreg.h