linux-kernel - Re: [PATCH 10/17] hyper-v: trace vmbus

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Date:   Sat, 4 Nov 2017 12:05:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     KY Srinivasan <kys@...rosoft.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "apw@...onical.com" <apw@...onical.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "leann.ogasawara@...onical.com" <leann.ogasawara@...onical.com>
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@...uxdriverproject.org] On
> > Behalf Of Steven Rostedt
> > Sent: Tuesday, October 31, 2017 6:10 AM
> > To: Greg KH <gregkh@...uxfoundation.org>
> > Cc: olaf@...fle.de; Stephen Hemminger <sthemmin@...rosoft.com>;
> > jasowang@...hat.com; linux-kernel@...r.kernel.org; apw@...onical.com;
> > marcelo.cerri@...onical.com; devel@...uxdriverproject.org; Vitaly
> > Kuznetsov <vkuznets@...hat.com>; leann.ogasawara@...onical.com
> > Subject: Re: [PATCH 10/17] hyper-v: trace vmbus_open()
> > 
> > On Tue, 31 Oct 2017 13:48:00 +0100
> > Greg KH <gregkh@...uxfoundation.org> 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,

greg k-h