Re: [PATCH 1/2] scsi: ufs: Add Multi-Circular Queue support

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On 7/28/2022 1:29 PM, Bart Van Assche wrote:
On 7/28/22 12:15, Asutosh Das (asd) wrote:
Hello John,

On 7/28/2022 12:10 PM, John Garry wrote:
On 19/07/2022 08:01, Can Guo wrote:
+
+    hba->nr_queues[HCTX_TYPE_DEFAULT] = num_possible_cpus();
+    hba->nr_queues[HCTX_TYPE_READ] = 0;
+    hba->nr_queues[HCTX_TYPE_POLL] = 1;
+
+    for (i = 0; i < HCTX_MAX_TYPES; i++)
+        host->nr_hw_queues += hba->nr_queues[i];
+
+    host->can_queue = hba->nutrs;
+    host->cmd_per_lun = hba->nutrs;
+
+    /* One more reserved for dev_cmd_queue */
+    hba->nr_hw_queues = host->nr_hw_queues + 1;
+

So this would mean that the host can accept .can_queue * .nr_hw_queues numbers of requests simultaneously - is that true?

That would mean that .can_queue * .nr_hw_queues numbers of request may be queued to the host.
Please can you elaborate if you see an issue.

Hi Asutosh,

The `host_tagset` flag has been introduced by John and Hannes some time ago. See also commit bdb01301f3ea ("scsi: Add host and host template flag 'host_tagset'"). This flag supports sharing tags across hardware queues and could be used to support UFSHCI 4.0 controllers that do not support the EXT_IID feature.

In order not to complicate the implementation further, I propose to fall back to the UFSHCI 3.0 compatibility mode for UFSHCI 4.0 controllers that do not support the EXT_IID feature.

To answer John's question: the maximum number of outstanding commands is 16 * hba->nutrs if EXT_IID is supported (EXT_IID is a four bits field). If the hardware queue index is encoded in the EXT_IID field, hba->nutrs is the number of commands per hardware queue.

Thanks,

Bart.

Thanks Bart, I wasn't aware of the background of John's Q. I will consider your proposal and get back.

-asd



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