Re: [RFC PATCH v2 2/3] bio: track timestamp of submitting bio the disk driver

[Christoph Hellwig <hch@infradead.org>]

On Tue, Mar 31, 2020 at 04:45:33PM +0800, Weiping Zhang wrote:
> Christoph Hellwig <hch@infradead.org> 于2020年3月31日周二 下午4:25写道：
> >
> > On Fri, Mar 27, 2020 at 02:28:59PM +0800, Weiping Zhang wrote:
> > > Change-Id: Ibb9caf20616f83e111113ab5c824c05930c0e523
> > > Signed-off-by: Weiping Zhang <zhangweiping@didiglobal.com>
> >
> > This needs a commit description and loose the weird change id.
> >
> OK, I rewirte commit description, it record the timestamp of issue bio
> to the disk driver,
> then we can get the delta time in rq_qos_done_bio. It's same as the D2C time
> of blktrace.
> > I also think oyu need to fins a way to not bloat the bio even more,
> > cgroup is a really bad offender for bio size.
> struct request {
>     u64 io_start_time_ns;
> also record this timestamp, I'll check if we can use it.

But except for a few exceptions bios are never issued directly to the
driver, requests are.  And the few exception (rsxx, umem) probably should
be rewritten to use requests.  And with generic_{start,end}_io_acct we
already have helpers to track bio based stats, which we should not
duplicate just for cgroups.