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

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Date:   Sat, 4 Nov 2017 15:09:48 +0000
From:   KY Srinivasan <kys@...rosoft.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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()



> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Saturday, November 4, 2017 4:05 AM
> To: KY Srinivasan <kys@...rosoft.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>; 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 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,

Thanks Greg.

K. Y
> 
> greg k-h