Re: [PATCH v6 03/28] scsi: core: Make the budget map optional

[Bart Van Assche <bvanassche@acm.org>]

On 10/22/25 1:29 AM, John Garry wrote:
> On 14/10/2025 21:15, Bart Van Assche wrote:
>> @@ -1360,6 +1361,9 @@ static inline int scsi_dev_queue_ready(struct 
>> request_queue *q,
>>   {
>>       int token;
>> +    if (!sdev->budget_map.map)
>> +        return INT_MAX;
> 
> For the record, I would not do things in this way.
> 
> The shost psuedo sdev does not need a budget, as mentioned.
> 
> However we complicate the code and add extra checks in the fastpath 
> (like in this function) by treating this sdev as special and not having 
> a budget.

Hi John,

The following patch series will be reposted after this patch series has
been merged: "[PATCH 0/3] Improve host-wide tag IOPS"
(https://lore.kernel.org/linux-scsi/20250910213254.1215318-1-bvanassche@acm.org/). 
Patch 3/3 from that series skips budget map
allocation if it is safe to do so. I don't think that it is possible to
skip budget map allocation in some cases without introducing an if-test.
In other words, the if-tests introduced by this patch will get more
users and will enable an important optimization for the fast path.

Thanks,

Bart.