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

[John Garry]

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....@redhat.com>
---
 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