Messages in this thread |  | | Date | Wed, 14 Nov 2001 09:11:29 +0100 | From | Jens Axboe <> | Subject | Re: [Lse-tech] SCSI io_request_lock patch |
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On Tue, Nov 13 2001, Jonathan Lahr wrote: > 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.
Yes I know, I wrote most of said code :-)
> What problem you do see with exporting block internals?
It's absolutely worthless. Look, it ties in with the points I made below. You are exporting the merge functions for instance, and setting them in the queue. This will cause scsi_merge not to use it's own functions, broken.
The make_request_fn addition could be ok, just needs to be cleaned a bit.
> > 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?
Not really, but I do think it could be a viable 2.4 alternative. For 2.5 we still want to do this the right way.
-- Jens Axboe
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