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
