Re: [PATCH V2 1/5] scsi: select reply queue from request's CPU

[John Garry <john.garry@xxxxxxxxxx>]

On 27/05/2019 16:02, Ming Lei wrote:
> Hisi_sas_v3_hw, hpsa, megaraid and mpt3sas use single blk-mq hw queue
> to submit request, meantime apply multiple private reply queues served as
> completion queue. The mapping between CPU and reply queue is setup via
> pci_alloc_irq_vectors_affinity(PCI_IRQ_AFFINITY) just like the usual
> blk-mq queue mapping.
>
> These drivers always use current CPU(raw_smp_processor_id) to figure out
> the reply queue. Switch to use request's CPU to get the reply queue,
> so we can drain in-flight request via blk-mq's API before the last CPU of
> the reply queue becomes offline.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
>  drivers/scsi/hisi_sas/hisi_sas_main.c       |  5 +++--
>  drivers/scsi/hpsa.c                         |  2 +-
>  drivers/scsi/megaraid/megaraid_sas_fusion.c |  4 ++--
>  drivers/scsi/mpt3sas/mpt3sas_base.c         | 16 ++++++++--------
>  include/scsi/scsi_cmnd.h                    | 11 +++++++++++
>  5 files changed, 25 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/scsi/hisi_sas/hisi_sas_main.c b/drivers/scsi/hisi_sas/hisi_sas_main.c
> index 8a7feb8ed8d6..ab9d8e7bfc8e 100644
> --- a/drivers/scsi/hisi_sas/hisi_sas_main.c
> +++ b/drivers/scsi/hisi_sas/hisi_sas_main.c
> @@ -471,9 +471,10 @@ static int hisi_sas_task_prep(struct sas_task *task,
>  		return -ECOMM;
>  	}
>
> +	/* only V3 hardware setup .reply_map */
>  	if (hisi_hba->reply_map) {
> -		int cpu = raw_smp_processor_id();
> -		unsigned int dq_index = hisi_hba->reply_map[cpu];
> +		unsigned int dq_index = hisi_hba->reply_map[
> +			scsi_cmnd_cpu(task->uldd_task)];

Hi Ming,

There is a problem here. For ATA commands in libsas, task->uldd_task is 
ata_queued_cmd *, and not a scsi_cmnd *. It comes from 
https://elixir.bootlin.com/linux/v5.2-rc2/source/drivers/scsi/libsas/sas_ata.c#L212

Please see this later code, where we have this check:
	if (task->uldd_task) {
		struct ata_queued_cmd *qc;

		if (dev_is_sata(device)) {
			qc = task->uldd_task;
			scsi_cmnd = qc->scsicmd;
		} else {
			scsi_cmnd = task->uldd_task;
		}
	}
	rc  = hisi_sas_slot_index_alloc(hisi_hba, scsi_cmnd);

I suppose that we could solve by finding scsi_cmnd * earlier in 
hisi_sas_task_prep().

>  		*dq_pointer = dq = &hisi_hba->dq[dq_index];
>  	} else {
> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
> index 1bef1da273c2..72f9edb86752 100644
> --- a/drivers/scsi/hpsa.c
> +++ b/drivers/scsi/hpsa.c
> @@ -1145,7 +1145,7 @@ static void __enqueue_cmd_and_start_io(struct ctlr_info *h,

[snip]

> diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
> index 76ed5e4acd38..ab60883c2c40 100644
> --- a/include/scsi/scsi_cmnd.h
> +++ b/include/scsi/scsi_cmnd.h
> @@ -332,4 +332,15 @@ static inline unsigned scsi_transfer_length(struct scsi_cmnd *scmd)
>  	return xfer_len;
>  }
>
> +static inline int scsi_cmnd_cpu(struct scsi_cmnd *scmd)
> +{
> +	if (!scmd || !scmd->request)
> +		return raw_smp_processor_id();
> +
> +	if (!scmd->request->mq_ctx)
> +		return raw_smp_processor_id();

nit: can we combine these tests? Or do you want a distinct check on 
scmd->request->mq_ctx, since blk_mq_rq_cpu() does not check it?

> +
> +	return blk_mq_rq_cpu(scmd->request);
> +}
> +
>  #endif /* _SCSI_SCSI_CMND_H */

Thanks

>