# Re: \[PATCH V4 00/12\] blktrace: output cgroup info

- From: Jens Axboe \<axboe@kernel.dk\>
- Date: 2017-06-28 16:54:39 
- List: linux-block
- Page: https://ratatoskr.run/linux-block/2017/06/5031896
- Thread: https://ratatoskr.run/linux-block/2017/06/5031858/t.md

```text
On 06/28/2017 10:53 AM, Shaohua Li wrote:
> On Wed, Jun 28, 2017 at 10:43:48AM -0600, Jens Axboe wrote:
>> On 06/28/2017 10:29 AM, Shaohua Li wrote:
>>> From: Shaohua Li <redacted>
>>>
>>> Hi,
>>>
>>> Currently blktrace isn't cgroup aware. blktrace prints out task name of current
>>> context, but the task of current context isn't always in the cgroup where the
>>> BIO comes from. We can't use task name to find out IO cgroup. For example,
>>> Writeback BIOs always comes from flusher thread but the BIOs are for different
>>> blk cgroups. Request could be requeued and dispatched from completely different
>>> tasks. MD/DM are another examples. This brings challenges if we want to use
>>> blktrace for performance tunning with cgroup enabled.
>>>
>>> This patchset try to fix the gap. We print out cgroup fhandle info in blktrace.
>>> Userspace can use open_by_handle_at() syscall to find the cgroup by fhandle. Or
>>> userspace can use name_to_handle_at() syscall to find fhandle for a cgroup and
>>> use a BPF program to filter out blktrace for a specific cgroup.
>>>
>>> The first 6 patches adds export operation handlers for kernfs, so userspace can
>>> use open_by_handle_at/name_to_handle_at to a kernfs file. Later patches make
>>> blktrace output cgroup info.
>>
>> Series looks fine to me. I don't know how you want to split or funnel it,
>> since it touches multiple different parts. Would it make sense to split this
>> series into two - one for the kernfs changes, and then a subsequent block
>> series that depend on that?
> 
> What's the best practice to do this without building errors? Ask Tejun
> to merge the first 7 patches first?

Yes, and then resend the block patches, just noting that dependency. Then
we can funnel them in like that.

-- 
Jens Axboe
```