Re: [RFC PATCH v3 2/3] blk-mq: Freeze and quiesce all queues for tagset in elevator_exit()

[Bart Van Assche]

On 3/11/21 12:21 AM, John Garry wrote:
> On 11/03/2021 00:58, Ming Lei wrote:
>> I think this way can't be accepted since switching one queue's scheduler
>> is nothing to do with other request queues attached to same HBA.
>>
>> This patch will cause performance regression because userspace may
>> switch scheduler according to medium or workloads, at that time other
>> LUNs will be affected by this patch.
> 
> Hmmm..that was my concern also. Do you think that it may cause a big
> impact? Depends totally on the workload, I suppose.
> 
> FWIW, it is useful though for solving both iterator problems.

Hi John,

How about replacing the entire patch series with the patch below? The
patch below has the following advantages:
- Instead of making the race window smaller, the race is fixed
  completely.
- No new atomic instructions are added to the block layer code.
- No early return is inserted in blk_mq_tagset_busy_iter().

Thanks,

Bart.