Re: [PATCH V4 08/12] blktrace: export cgroup info in trace

Steven Rostedt
2017-06-28T16:56:18Z

On Wed, 28 Jun 2017 09:29:58 -0700
Shaohua Li <shli@kernel.org> wrote:

> From: Shaohua Li <shli@fb.com>
>
> 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 patch tries 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.
>
> We add a new 'blk_cgroup' trace option for blk tracer. It's default off.
> Application which doesn't know the new option isn't affected. When it's
> on, we output fhandle info right after blk_io_trace with an extra bit
> set in event action. So from application point of view, blktrace with
> the option will output new actions.
>
> I didn't change blk trace event yet, since I'm not sure if changing the
> trace event output is an ABI issue. If not, I'll do it later.
>
> Signed-off-by: Shaohua Li <shli@fb.com>
> ---
> include/uapi/linux/blktrace_api.h | 3 +
> kernel/trace/blktrace.c | 231 ++++++++++++++++++++++++++------------
> 2 files changed, 161 insertions(+), 73 deletions(-)

Doing a quick scan of the patch, nothing sticks out as an issue to me.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve