Re: [PATCH RFC v3 2/7] ata: libata-scsi: Add ata_internal_queuecommand()

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On 27/10/2022 23:25, Damien Le Moal wrote:
So we have this overall flow:

ata_exec_internal_sg():
   -> alloc request
   -> blk_execute_rq_nowait()
       ... -> scsi_queue_rq()
		-> sht->reserved_queuecommd()
			-> ata_internal_queuecommand()

And then we have ata_internal_queuecommand() -> ata_sas_queuecmd() ->
ata_scsi_queue_internal() -> ata_qc_issue().

Hope it makes sense.
OK. Got it.
However, ata_exec_internal_sg() being used only from EH context with the
queue quiesced, will blk_execute_rq_nowait() work ? Is there an exception
for internal reserved tags ?


Well, yeah. So if some error happens and EH kicks in, then full queue depth of requests may be allocated. I have seen this for NCQ error. So this is why I make in very first patch change allow us to allocate reserved request from sdev request queue even when budget is fully allocated.

Please also note that for AHCI, I make reserved depth =1, while for SAS controllers it is greater. This means that in theory we could alloc > 1x reserved command for SATA disk, but I don't think it matters.

Thanks,
John



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