Messages in this thread | | | Date | Fri, 29 Jul 2022 09:43:21 -0700 | Subject | Re: [PATCH 1/2] scsi: ufs: Add Multi-Circular Queue support | From | "Asutosh Das (asd)" <> |
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Hi Bart,
On 7/28/2022 2:07 PM, Asutosh Das (asd) wrote: > 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. >
I went through the change and fwiu of your proposal is to use host_tagset = 1 if HC doesn't support EXT_IID capability. That way tags would be shared across 16 HWQs (4-bit IID encoding the queue-ids). That would also mean that the hba->nutrs would have to be adjusted such that the tags(8-bit) don't exceed 255.
Summarily, if EXT_IID is not supported: host_tagset = 1, maximum configurable hba->nutrs = 16, maximum configurable nr_hw_queues = 16. maximum number of outstanding commands to host = 16 x 16 = 256.
if EXT_IID is supported: host_tagset = 0, maximum confiugrable hba-nutrs = 255, maximum configurable nr_hw_queues = 255.
Please let me know if I'm missing something.
Thank you, -asd
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