Messages in this thread | | | From | John Garry <> | Subject | Re: [PATCH 6/6] scsi: hisi_sas: Expose multiple hw queues for v3 as experimental | Date | Tue, 12 Nov 2019 13:54:44 +0000 |
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>> >> I mentioned in the thread "blk-mq: improvement on handling IO during CPU >> hotplug" that I was using this series to test that patchset. >> >> So just with this patchset (and without yours), I get what looks like some >> IO errors in the LLDD. The error is an underflow error. I can't figure out >> what is the cause. >
Hi Ming,
> Can you post the error log? Or interpret the 'underflow error' from hisi > sas or scsi viewpoint?
The check here fails: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/scsi/libsas/sas_scsi_host.c?h=v5.4-rc7#n57
Indeed, no data is received.
> >> >> I'm wondering if the SCSI command is getting corrupted someway. > > Why do you think the command is corrupted?
I considered that the underflow may occur if we were to clobber a SCSI command/request from another hctx and zero some fields, which is detected as an underflow. But that's just guessing.
However do I find if I set shost->can_queue = HISI_SAS_MAX_COMMANDS / #queues, then no issue. But maybe that's a coincidence. For this, total queue depth = HISI_SAS_MAX_COMMANDS. I don't see the impact of that.
I need to test that more.
> >> >>>> + if (expose_mq_experimental) { >>>> + shost->can_queue = HISI_SAS_MAX_COMMANDS; >>>> + shost->cmd_per_lun = HISI_SAS_MAX_COMMANDS; >>> The above is contradictory with current 'nr_hw_queues''s meaning, >>> see commit on Scsi_Host.nr_hw_queues. >>> >> >> Right, so I am generating the hostwide tag in the LLDD. And the Scsi >> host-wide host_busy counter should ensure that we don't pump too much IO to >> the HBA. > > Even without the host-wide host_busy, your approach should work if you > build the hisi sas tag correctly(uniquely), just not efficiently.
Yes, I do that.
I'd > suggest you to collect trace and observe if request with expected hisi sas > tag is sent to hardware. >
I can add some debug for that. What trace do you mean?
> BTW, the patch of 'scsi: core: avoid host-wide host_busy counter for scsi_mq' > will be merged to v5.5 if everything is fine. > > https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git/commit/?h=5.5/scsi-queue&id=6eb045e092efefafc6687409a6fa6d1dabf0fb69
Yeah, it seems a good change.
Thanks, John
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