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

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Message-ID: <20171030084537.GA14865@kroah.com>
Date:   Mon, 30 Oct 2017 09:45:37 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kys@...rosoft.com, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        jasowang@...hat.com, leann.ogasawara@...onical.com,
        marcelo.cerri@...onical.com, sthemmin@...rosoft.com
Subject: Re: [PATCH 10/17] hyper-v: trace vmbus_open()

On Mon, Oct 30, 2017 at 09:16:19AM +0100, Vitaly Kuznetsov wrote:
> Greg KH <gregkh@...uxfoundation.org> writes:
> 
> > On Sun, Oct 29, 2017 at 12:21:09PM -0700, kys@...hange.microsoft.com wrote:
> >> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> >> 
> >> Add tracepoint to CHANNELMSG_OPENCHANNEL sender.
> >> 
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> >> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> >> ---
> >>  drivers/hv/channel.c  |  2 ++
> >>  drivers/hv/hv_trace.h | 27 +++++++++++++++++++++++++++
> >>  2 files changed, 29 insertions(+)
> >> 
> >> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> >> index a406beb10dd0..739b3fe1e0fb 100644
> >> --- a/drivers/hv/channel.c
> >> +++ b/drivers/hv/channel.c
> >> @@ -185,6 +185,8 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
> >>  	ret = vmbus_post_msg(open_msg,
> >>  			     sizeof(struct vmbus_channel_open_channel), true);
> >>  
> >> +	trace_vmbus_open(open_msg, ret);
> >
> > Why add tracepoints for things that ftrace can handle automatically?
> 
> This series adds pretty prints for structures printing what is needed
> and in the right format significantly simplifying debugging. And it
> wouldn't make sense to add tracepoints to *some* messages-related
> functions and skip others where parsing is more trivial.

Tracepoints add memory usage and take up real space.  If you don't need
them for something, as there are other ways to already get the
information needed, why add new ones that you now need to drag around
for all time?

thanks

greg k-h