From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751945AbdJ3Obj (ORCPT ); Mon, 30 Oct 2017 10:31:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:37018 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751374AbdJ3Obi (ORCPT ); Mon, 30 Oct 2017 10:31:38 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B9972192A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Mon, 30 Oct 2017 10:31:34 -0400 From: Steven Rostedt To: Greg KH Cc: Vitaly Kuznetsov , kys@microsoft.com, linux-kernel@vger.kernel.org, devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com, jasowang@redhat.com, leann.ogasawara@canonical.com, marcelo.cerri@canonical.com, sthemmin@microsoft.com Subject: Re: [PATCH 10/17] hyper-v: trace vmbus_open() Message-ID: <20171030103134.22086c4e@gandalf.local.home> In-Reply-To: <20171030103220.GA30988@kroah.com> References: <20171029192030.12356-1-kys@exchange.microsoft.com> <20171029192116.12466-1-kys@exchange.microsoft.com> <20171029192116.12466-10-kys@exchange.microsoft.com> <20171029205958.GA30187@kroah.com> <877evdyrsc.fsf@vitty.brq.redhat.com> <20171030084537.GA14865@kroah.com> <873761ymnu.fsf@vitty.brq.redhat.com> <20171030103220.GA30988@kroah.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 30 Oct 2017 11:32:20 +0100 Greg KH wrote: > On Mon, Oct 30, 2017 at 11:07:01AM +0100, Vitaly Kuznetsov wrote: > > Greg KH writes: > > > > > On Mon, Oct 30, 2017 at 09:16:19AM +0100, Vitaly Kuznetsov wrote: > > >> Greg KH writes: > > >> > > >> > On Sun, Oct 29, 2017 at 12:21:09PM -0700, kys@exchange.microsoft.com wrote: > > >> >> From: Vitaly Kuznetsov > > >> >> > > >> >> Add tracepoint to CHANNELMSG_OPENCHANNEL sender. > > >> >> > > >> >> Signed-off-by: Vitaly Kuznetsov > > >> >> Signed-off-by: K. Y. Srinivasan > > >> >> --- > > >> >> 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? > > > > > > > Are you opposed to the series as a whole (AKA 'no tracepoints in > > drivers') or only to some tracepoints we add here? > > I'm opposed to adding tracepoints for things that are not needed as you > can get the same info already today without the tracepoint. I looked at this specific tracepoint, and I don't see how to get the information from the current tracing infrastructure. Maybe an eBPF program attached to a kprobe here might work. But the tracepoint data looks like this: + TP_STRUCT__entry( + __field(u32, child_relid) + __field(u32, openid) + __field(u32, gpadlhandle) + __field(u32, target_vp) + __field(u32, offset) + __field(int, ret) + ), + TP_fast_assign( + __entry->child_relid = msg->child_relid; + __entry->openid = msg->openid; + __entry->gpadlhandle = msg->ringbuffer_gpadlhandle; + __entry->target_vp = msg->target_vp; + __entry->offset = msg->downstream_ringbuffer_pageoffset; + __entry->ret = ret; + ), I don't see how that information can be extracted easily without a tracepoint here. Am I missing something? -- Steve > > I'm not opposed to tracepoints in drivers as it's up to the maintainer > to have to manage them over the long-term and the issues that surround > them... > >