RE: [PATCH 10/17] hyper-v: trace vmbus_open()

[KY Srinivasan]

> -----Original Message-----
> From: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx]
> Sent: Saturday, November 4, 2017 4:05 AM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>; olaf@xxxxxxxxx; Stephen
> Hemminger <sthemmin@xxxxxxxxxxxxx>; jasowang@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; apw@xxxxxxxxxxxxx; marcelo.cerri@xxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>;
> leann.ogasawara@xxxxxxxxxxxxx
> Subject: Re: [PATCH 10/17] hyper-v: trace vmbus_open()
> 
> On Wed, Nov 01, 2017 at 05:43:08PM +0000, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: devel [mailto:driverdev-devel-bounces@xxxxxxxxxxxxxxxxxxxxxx]
> On
> > > Behalf Of Steven Rostedt
> > > Sent: Tuesday, October 31, 2017 6:10 AM
> > > To: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: olaf@xxxxxxxxx; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>;
> > > jasowang@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> apw@xxxxxxxxxxxxx;
> > > marcelo.cerri@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; Vitaly
> > > Kuznetsov <vkuznets@xxxxxxxxxx>; leann.ogasawara@xxxxxxxxxxxxx
> > > Subject: Re: [PATCH 10/17] hyper-v: trace vmbus_open()
> > >
> > > On Tue, 31 Oct 2017 13:48:00 +0100
> > > Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > > > I don't see how that information can be extracted easily without a
> > > > > tracepoint here. Am I missing something?
> > > >
> > > > Wasn't one of the outcomes of the conference last week the fact that
> for
> > > > ftrace + ebpf we could get access to the structures of the function
> > > > parameters?  Or that work would soon be showing up?
> > >
> > > I told Linus that I'll start building an infrastructure on function
> > > tracing to see what we can do. But it may be very limited in features.
> > > I don't believe eBPF can follow arbitrary data structure pointers
> > > without helper functions. Which doesn't exist for this type of code yet.
> > >
> > > >
> > > > It just feels "wrong" to add a tracepoint for a function call, like it
> > > > is a duplication of work/functionality we already have.
> > >
> > > We don't already have it. We may have something in a year (or two) that
> > > may be able to get all the data that is requested here. But it's going
> > > to take lots of RFC patch sets and brain storming to come up with
> > > something that everyone is satisfied with.
> > >
> > > In other words, the functionality is currently in vaporware state.
> >
> > Greg,
> >
> > The added memory overhead is very minimal, and the added tracing
> support is extremely useful for
> > our debugging. If you don't mind, I would like to have this tracing support.
> 
> Ok, it's your subsystem, you get to handle the long-term maintenance of
> these :)
> 
> Now merged,

Thanks Greg.

K. Y
> 
> greg k-h