On 24.12.20 г. 23:11 ч., René Rebe wrote:
> Hi Josef,
>
>> On 24. Dec 2020, at 19:09, Josef Bacik <[email protected]> wrote:
>>
>> On 12/21/20 2:45 PM, René Rebe wrote:
>>> Hey there,
>>> as a long time btrfs user I noticed some some things became very slow
>>> w/ Linux kernel 5.10. I found a very simple test case, namely extracting
>>> a huge tarball like:
>>> tar xf /usr/src/t2-clean/download/mirror/f/firefox-84.0.source.tar.zst
>>> Why my external, USB3 road-warrior SSD on a Ryzen 5950x this
>>> went from ~15 seconds w/ 5.9 to nearly 5 minutes in 5.10, or 2000%
>>> To rule out USB, I also tested a brand new PCIe 4.0 SSD, with
>>> a similar, albeit not as shocking regression from 5.2 seconds
>>> to ~34 seconds or∫~650%.
>>> Somehow testing that in a VM did over virtio did not produce
>>> as different results, although it was already 35 seconds slow
>>> with 5.9.
>>> # first bad commit: [38d715f494f2f1dddbf3d0c6e50aefff49519232]
>>> btrfs: use btrfs_start_delalloc_roots in shrink_delalloc
>>> Now just this single commit does obviously not revert cleanly,
>>> and I did not have the time today to look into the rather more
>>> complex code today.
>>> I hope this helps improve this for the next release, maybe you
>>> want to test on bare metal, too.
>>
>> Alright to close the loop with this, this slipped through the cracks because
>> I was doing a lot of performance related work, and specifically had been
>> testing with these patches on top of everything
>>
>> https://lore.kernel.org/linux-btrfs/[email protected]/
>>
>> These patches bring the performance up to around 40% higher than baseline
>
> I indeed tested the linux-btrfs for-5.11 and found the performance some 50%
> better. I would hope that can be brought back to 5.9 levels sometime soon ;-)
Do you mean 50% better as compared to 5.9?
>
>> . In the meantime we'll probably push this partial revert into 5.10 stable
>> so performance isn't sucking in the meantime. Thanks,
>
> That certainly makes sense for the LTS kernel series.
>
> Thanks for looking into this,
> Merry Christmas,
> René Rebe
>
