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    DateMon, 12 Nov 2001 13:09:02 -0800
    FromJonathan Lahr <>
    SubjectSCSI io_request_lock patch
    This is a request for comments on the patch described below which 
    implements a revised approach to reducing io_request_lock contention 
    in 2.4.
    
    This new version of the io_request_lock patch (siorl-v0) is available
    at http://sourceforge.net/projects/lse/.  It employs the same
    concurrent request queueing scheme as the iorlv0 patch but isolates 
    code changes to the SCSI subsystem and engages the new locking scheme 
    only for SCSI drivers which explicitly request it.  I took this more 
    restricted approach after additional development based on comments from 
    Jens and others indicated that iorlv0 impacted the IDE subsystem and
    was unnecessarily broad in general.
    
    The siorl-v0 patch allows drivers to enable concurrent queueing through 
    the concurrent_queue field in the Scsi_Host_Template which is copied to 
    the request queue.  It creates SCSI-specific versions of generic block 
    i/o functions used by the SCSI subsystem and modifies them to conditionally 
    engage the new locking scheme based on this field.  It allows control over 
    which drivers use concurrent queueing and preserves original block i/o 
    behavior by default.
    
    I tested this patch with aic7xxx and lpfc drivers, and regression tested 
    it with IDE disk and CDROM drivers.  Any feedback would be appreciated.
    
    Thanks,
    Jonathan
    
    -- 
    Jonathan Lahr
    IBM Linux Technology Center
    Beaverton, Oregon
    lahr@us.ibm.com
    503-578-3385
    
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