On 4/8/2021 1:46 AM, Hannes Reinecke wrote:

On 4/7/21 1:06 AM, Muneendra wrote:

quoted

From: Gaurav Srivastava <redacted>

...

quoted

+        /* while the read lock was released, in case the entry was */
+        /* added by other context or is in process of being added */
+        if (vmp && vmp->flag & LPFC_VMID_REGISTERED) {
+            lpfc_vmid_update_entry(vport, cmd, vmp, tag);
+            write_unlock(&vport->vmid_lock);
+            return 0;
+        } else if (vmp && vmp->flag & LPFC_VMID_REQ_REGISTER) {
+            write_unlock(&vport->vmid_lock);
+            return -EBUSY;
+        }
+
+        /* else search and allocate a free slot in the hash table */
+        if (vport->cur_vmid_cnt < vport->max_vmid) {
+            for (i = 0; i < vport->max_vmid; ++i) {
+                vmp = vport->vmid + i;
+                if (vmp->flag == LPFC_VMID_SLOT_FREE) {
+                    vmp = vport->vmid + i;

delete this last line and adjust parens - really odd that it replicates 
the assignment 2 lines earlier.

quoted

+                    break;
+                }
+            }

I would prefer that if the table is expended and no slots free, that 
-ENOMEM is returned here. Rather than falling down below and qualifying 
by slot free, then by pending (set only if slot free).  I can't believe 
there is a reason the idle timer has to be started if no slots free as 
all the other fail cases don't bother with it.

This also helps indentation levels below.

quoted

+        } else {
+            write_unlock(&vport->vmid_lock);
+            return -ENOMEM;
+        }
+
+        if (vmp && (vmp->flag == LPFC_VMID_SLOT_FREE)) {
+            /* Add the vmid and register  */
+            lpfc_put_vmid_in_hashtable(vport, hash, vmp);
+            vmp->vmid_len = len;
+            memcpy(vmp->host_vmid, uuid, vmp->vmid_len);
+            vmp->io_rd_cnt = 0;
+            vmp->io_wr_cnt = 0;
+            vmp->flag = LPFC_VMID_SLOT_USED;
+
+            vmp->delete_inactive =
+                vport->vmid_inactivity_timeout ? 1 : 0;
+
+            /* if type priority tag, get next available vmid */
+            if (lpfc_vmid_is_type_priority_tag(vport))
+                lpfc_vmid_assign_cs_ctl(vport, vmp);
+
+            /* allocate the per cpu variable for holding */
+            /* the last access time stamp only if vmid is enabled */
+            if (!vmp->last_io_time)
+                vmp->last_io_time =
+                    __alloc_percpu(sizeof(u64),
+                           __alignof__(struct
+                                   lpfc_vmid));
+
+            /* registration pending */
+            pending = 1;
+        } else {
+            rc = -ENOMEM;
+        }
+        write_unlock(&vport->vmid_lock);
+
+        /* complete transaction with switch */
+        if (pending) {
+            if (lpfc_vmid_is_type_priority_tag(vport))
+                rc = lpfc_vmid_uvem(vport, vmp, true);
+            else
+                rc = lpfc_vmid_cmd(vport,
+                           SLI_CTAS_RAPP_IDENT,
+                           vmp);
+            if (!rc) {
+                write_lock(&vport->vmid_lock);
+                vport->cur_vmid_cnt++;
+                vmp->flag |= LPFC_VMID_REQ_REGISTER;
+                write_unlock(&vport->vmid_lock);
+            }
+        }
+
+        /* finally, enable the idle timer once */
+        if (!(vport->phba->pport->vmid_flag & LPFC_VMID_TIMER_ENBLD)) {
+            mod_timer(&vport->phba->inactive_vmid_poll,
+                  jiffies +
+                  msecs_to_jiffies(1000 * LPFC_VMID_TIMER));
+            vport->phba->pport->vmid_flag |= LPFC_VMID_TIMER_ENBLD;
+        }
+    }
+    return rc;
+}
+
+/*
+ * lpfc_is_command_vm_io - get the uuid from blk cgroup
+ * @cmd:Pointer to scsi_cmnd data structure
+ * Returns uuid if present if not null
+ */
+static char *lpfc_is_command_vm_io(struct scsi_cmnd *cmd)
+{
+    char *uuid = NULL;
+
+    if (cmd->request) {
+        if (cmd->request->bio)
+            uuid = blkcg_get_fc_appid(cmd->request->bio);
+    }
+    return uuid;
+}
+
  /**
   * lpfc_queuecommand - scsi_host_template queuecommand entry point
   * @shost: kernel scsi host pointer.

@@ -5288,6 +5437,7 @@ lpfc_queuecommand(struct Scsi_Host *shost, 

struct scsi_cmnd *cmnd)
      int err, idx;
  #ifdef CONFIG_SCSI_LPFC_DEBUG_FS
      uint64_t start = 0L;
+    u8 *uuid = NULL;
      if (phba->ktime_on)
          start = ktime_get_ns();

@@ -5415,6 +5565,25 @@ lpfc_queuecommand(struct Scsi_Host *shost, 

struct scsi_cmnd *cmnd)
      }
+    /* check the necessary and sufficient condition to support VMID */
+    if (lpfc_is_vmid_enabled(phba) &&
+        (ndlp->vmid_support ||
+         phba->pport->vmid_priority_tagging ==
+         LPFC_VMID_PRIO_TAG_ALL_TARGETS)) {
+        /* is the IO generated by a VM, get the associated virtual */
+        /* entity id */
+        uuid = lpfc_is_command_vm_io(cmnd);
+
+        if (uuid) {
+            err = lpfc_vmid_get_appid(vport, uuid, cmnd,
+                (union lpfc_vmid_io_tag *)
+                    &lpfc_cmd->cur_iocbq.vmid_tag);
+            if (!err)
+                lpfc_cmd->cur_iocbq.iocb_flag |= LPFC_IO_VMID;
+        }
+    }
+
+    atomic_inc(&ndlp->cmd_pending);
  #ifdef CONFIG_SCSI_LPFC_DEBUG_FS
      if (unlikely(phba->hdwqstat_on & LPFC_CHECK_SCSI_IO))
          this_cpu_inc(phba->sli4_hba.c_stat->xmt_io);

And that's the bit which I don't particular like.

Essentially we'll have to inject additional ELS commands _on each I/O_ 
to get a valid VMID.
Where there are _so_ many things which might get wrong, causing an I/O 
stall.

I don't follow you - yes ELS's are injected when there isn't an entry 
for the VM, but once there is, there isn't further ELS's. That is the 
cost. as we don't know what uuid's I/O will be sent to before hand, so 
it has to be siphoned off during the I/O flow.  I/O's can be sent 
non-tagged while the ELS's are completing (and there aren't multiple 
sets of ELS's as long as it's the same uuid), which is fine.

so I disagree with "_on each I/O_".

I would have vastly preferred if we could _avoid_ having to do 
additional ELS commands for VMID registration in the I/O path
(ie only allow for I/O with a valid VMID), and reject the I/O otherwise 
until VMID registration is complete.

IE return 'BUSY' (or even a command retry?) when no valid VMID for this 
particular I/O is found, register the VMID (preferably in another 
thread), and restart the queue once the VMID is registered.

Why does it bother you with the I/O path ?  It's actually happening in 
parallel with no real relation between the two.

I seriously disagree with reject if no vmid tag. Why?  what do you gain 
? This actually introduces more disruption than the parallel flow with 
the ELSs.   Also, after link bounce, where all VMID's have to be done, 
it adds a stall window after link up right when things are trying to 
resume after rports rejoin. Why add the i/o rebouncing ? There no real 
benefit. Issuing a few untagged I/O doesn't hurt.

That way we have a clear separation, and the I/O path will always work 
with valid VMIDs.

Hmm?

Cheers,

Hannes

-- james