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

Shaohua Li
2017-06-28T16:53:27Z

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 <shli@fb.com>
> >
> > 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?

Thanks,
Shaohua