Messages in this thread | | | Date | Thu, 27 Jan 2000 20:35:47 +0200 (IST) | From | Gadi Oxman <> | Subject | Re: ide-scsi problems with multiple CD-Rs on same channel (2.2.14) |
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Hi,
> Gadi, > > Do you what this added?
This patches play with our "drive scheduling" decisions when several drives are serialized by the same hwgroup.
In 2.0.x, we used to put requests for both drives on the interface in the same queue, and finish all requests for one drive before switching to the other drive. Somewhere in 2.1.x we added per-drive queues, and started to play with how to share the interface bandwidth between them fairly, in an attempt to prevent a slow device from starving a fast device which shares the same channel.
The current algorithm in the kernel tries to measure the last request service time of a drive, and then give the other drive the bus for the same amount of time before taking it back from him. It also provides service for devices capable of "disconnecting" using DSC overlap. The patches instead try to revert to a simple "one request for drive 1", then "one request for drive 2" round robin algorithm.
Tkil's setup is unique in that three of the four IDE devices have real time constrains -- if we fail to service a CD-R in time, we make a coaster. In addition to that, the fourth IDE device is actually the source drive for all the three and shares a bus with one of them. This kind of setup really triggers and let us see inefficiencies in various places.
Cheers,
GAdi
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