Messages in this thread |  | | | Date | Tue, 13 Nov 2001 10:42:10 -0800 | | From | Jonathan Lahr <> | | Subject | Re: [Lse-tech] SCSI io_request_lock patch |
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Jens Axboe [axboe@suse.de] wrote: > 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
The duplication is a reasonable starting point for SCSI-specific functions. The block i/o design provides for exactly this type of tailoring through function pointers installed in request_queue.
What problem you do see with 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
I will investigate the above comments further.
> At least you are not breaking anything other than SCSI this time...
Do you think the separation of SCSI from generic block i/o code and the driver-activated control of concurrent queueing provides a path for future work to reduce io_request_lock contention in SCSI/FC?
-- Jonathan Lahr IBM Linux Technology Center Beaverton, Oregon lahr@us.ibm.com 503-578-3385
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