Re: [PATCH v7 4/9] nvme-multipath: add support for latency I/O policy

[Nilay Shroff <nilay@linux.ibm.com>]

On 8/11/26 3:56 PM, John Garry wrote:
> On 10/08/2026 18:25, Nilay Shroff wrote:
>>>
>>> iops: (groupid=0, jobs=10): err= 0: pid=821: Mon Aug 10 08:08:28 2026
>>>     read: IOPS=9239, BW=36.1MiB/s (37.8MB/s)(1434MiB/39744msec)
>>>       slat (usec): min=25, max=110836, avg=129.22, stdev=537.18
>>>
>>> Note that I do have many heavy kernel debug options enabled, like kasan and kmemleak, which may influence this.
>>>
>>
>> Thanks for testing. Given that you're running with KASAN, kmemleak, and other
>> heavy debug options enabled, I think this is expected. Those configurations
>> can significantly increase I/O completion latency, causing some samples to
>> exceed the 1-second threshold. The warning is also rate-limited to avoid
>> flooding the log. That said, still if it's causing a lot of noise in the logs
>> then we could change it to dev_dbg_ratelimited() from dev_warn_ratelimited().
> 
> Note they these warnings go away when I turn off those debug options, as expected.
> 
> The max latency I was seeing was ~1.2 seconds. Maybe you can just increase this limit for ignoring the sample. Or make it a dev_warn_once(). Or control the warn print rate with DEFINE_RATELIMIT_STATE.

I think we could make it dev_warn_once() as we also increment the stat
counter nr_ignored when we hit this case. So user could always interrogate
the stat counter to find num of samples those were ignored.

Thanks,
--Nilay