From: Jens A. <ax...@su...> - 2001-11-13 08:23:34
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On Mon, Nov 12 2001, Jonathan Lahr wrote: > > 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. Sorry Jonathan, but this is even more broken than the last patch. In different ways. In no particular order: o You are duplicating way too much code and exporting block internals o You are breaking SCSI merge completely, why on earth are you suddenly using ll_*_merge functions for SCSI?! o scsi_make_request need not worry about head active o scsi_make_request can safe the q->*_merge indirect o scsi_dispatch_cmd() io_request_lock removal looks racy At least you are not breaking anything other than SCSI this time... -- Jens Axboe |