Re: [PATCH 0/5] btrfs: scrub: improve the scrub performance

[David Sterba <dsterba@suse.cz>]

On Fri, Jul 28, 2023 at 02:38:35PM +0200, Martin Steigerwald wrote:
> Qu Wenruo - 28.07.23, 13:14:03 CEST:
> > The first 3 patches would greately improve the scrub read performance,
> > but unfortunately it's still not as fast as the pre-6.4 kernels.
> > (2.2GiB/s vs 3.0GiB/s), but still much better than 6.4 kernels
> > (2.2GiB vs 1.0GiB/s).
> 
> Thanks for the patch set.
> 
> What is the reason for not going back to the performance of the pre-6.4 
> kernel? Isn't it possible with the new scrubbing method? In that case 
> what improvements does the new scrubbing code have that warrant to have 
> a lower performance?

Lower performance was not expected and needs to be brought back. A minor
decrease would be tolerable but that's something around 5%, not 60%.

> Just like to understand the background of this a bit more. I do not mind 
> a bit lower performance too much, especially in case it is outweighed by 
> other benefits.

The code in scrub was from 3.0 times and since then new features have
been implemented, extending the code became hard over time so a bigger
update was done restructuring how the IO is done.