[bug-report] 5-9% FIO randomwrite ext4 perf regression on 6.12.y kernel

[Jens Axboe]

On 11/20/24 9:57 PM, Christoph Hellwig wrote:
> On Wed, Nov 20, 2024 at 06:20:12PM -0700, Jens Axboe wrote:
>> There's no way that commit is involved, the test as quoted doesn't even
>> touch write zeroes. Hence if there really is a regression here, then
>> it's either not easily bisectable, some error was injected while
>> bisecting, or the test itself is bimodal.
> 
> ext4 actually has some weird lazy init code using write zeroes.  So
> if the test actually wasn't a steady state one but only run for a short
> time after init, and the mentioned commit dropped the intel hack for
> deallocate as write zeroes it might actually make a difference.

Ah good point, I forgot about the ext4 lazy init. But any test should
surely quiesce that first, not great to have background activity with
that.

-- 
Jens Axboe