Re: [linux-next:master] [btrfs] 551e510a97: fio.write_iops 12.4% improvement

hi, Mark,

On Fri, May 29, 2026 at 11:39:39AM +0100, Mark Harmstone wrote:
> Thanks for this Oliver, mind if I offer some constructive criticism?
> 
> 1) Your fio script has both "buffered=0" and "direct=0", which are
> contradictory. It looks like in this case fio treats it as "direct=1",
> but this probably should be explicit.
> 
> 2) Recent versions of btrfs fallback to buffered I/O unless nodatasum is
> set. You probably want to add:
> 
> 	mkdir /fs/sda1/nocow
> 	chattr +C /fs/sda1/nocow
> 
> and then change the directory to be /fs/sda1/nocow.
> 
> 3) My experience is that for FS performance testing, the only way to get
> useful figures is by PCI passthrough of an NVMe drive. Otherwise the VM
> overhead is enough to skew the figures.

thanks a lot for these education to us! we will investigate further how to
improve our tests. thanks again!

> 
> Mark
>