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

From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Anand Jain <anand.jain@oracle.com>, Qu Wenruo <wqu@suse.com>,
	linux-btrfs@vger.kernel.org, fstests@vger.kernel.org
Subject: Re: [PATCH] btrfs: add a test case to verify scrub speed throttle works
Date: Thu, 5 Jan 2023 07:17:02 +0800	[thread overview]
Message-ID: <b35e20df-9c9d-04b2-4830-46affac5c48f@gmx.com> (raw)
In-Reply-To: <151e5c83-6de6-9950-d1ce-8a375acea356@oracle.com>

On 2023/1/5 06:17, Anand Jain wrote:
> 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%?

Sounds great.

Thanks,
Qu
> 
> -Anand
> 
> 