Re: [PATCH V5 00/11] blktrace: output cgroup info

From: Jens Axboe
Date: Wed Jul 12 2017 - 18:51:05 EST

On 07/12/2017 12:49 PM, Shaohua Li wrote:
> From: Shaohua Li <shli@xxxxxx>
> 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.

Added for 4.14, thanks Shaohua.

Jens Axboe