Re: [Qemu-devel] [PATCH v2] lsi: Reselection needed to remove pending commands from queue

[Paolo Bonzini]

On 22/10/2018 23:28, George Kennedy wrote:
> As you suggested I moved the loading of "s->resel_dsp" down to the "Wait 
> Reselect"
> case. The address of the Reselection Scripts, though, is contained in "s->dsp 
> - 8"
> and not in s->dnad.

Are you sure?  s->dsp - 8 should be the address of the Wait Reselect
instruction itself.  But you're right that s->dnad is the address at
which to jump "if the LSI53C895A is selected before being reselected"
(as the spec puts it) so the reselection DSP should be just s->dsp.

> The reason the timeout is needed is that under heavy IO some pending commands
> stay on the pending queue longer than the 30 second command timeout set by the
> linux upper layer scsi driver (sym53c8xx). When command timeouts occur, the
> upper layer scsi driver sends SCSI Abort messages to remove the timed out
> commands. The command timeouts are caused by the fact that under heavy IO,
> lsi_reselect() in qemu "hw/scsi/lsi53c895a.c" is not being called before the
> upper layer scsi driver 30 second command timeout goes off.
> 
> If lsi_reselect() were called more frequently, the command timeout problem 
> would
> probably not occur. There are a number of places where lsi_reselect() is 
> supposed
> to get called (e.g. at the end of lsi_update_irq()), but the only place that I
> have observed lsi_reselect() being called is from lsi_execute_script() when
> lsi_wait_reselect() is called because of a SCRIPT "Wait Select" IO 
> Instruction.

Reselection should only happen when the target needs access to the bus,
which is when I/O has finished.  There should be no need for such a
deadline; reselection should already be happening at the right time when
lsi_transfer_data calls lsi_queue_req, which in turn calls lsi_reselect.

Maybe many of the places that call lsi_irq_on_rsl(s) also need to check
s->want_resel?

Paolo