Re: [PATCH] btrfs: add a test case to verify scrub speed throttle works

[Anand Jain <anand.jain@oracle.com>]

On 1/4/23 16:21, Qu Wenruo wrote:
> We introduced scrub speed throttle in commit eb3b50536642 ("btrfs: scrub:
> per-device bandwidth control"),  but it is not that well documented
> (e.g. what's the unit of the sysfs interface), nor tested by any test
> case.
> 
> This patch will add a test case for this functionality.
> 
> The test case itself is pretty straightforward:
> 
> - Fill the fs with 2G file as scrub workload
> - Set scrub speed limit to 50MiB/s
> - Scrub and compare the reported rate against above 50MiB/s throttle
> 
> However the test case has an assumption that the underlying disk must be
> faster than our 50MiB/s, which should be pretty common in
> baremetal/exclusive VMs.
> But for cloud environment it's not ensured 100%, thus the test case is
> not included in auto group to avoid false alerts.


Why not scrub the data twice: first to determine the speed, and then to 
check if it can be throttled to ~50%?

-Anand