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Date:   Sun, 21 Jan 2018 17:01:40 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc:     devicetree@vger.kernel.org,
        Tyrel Datwyler <tyreld@linux.vnet.ibm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-renesas-soc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/1] of: introduce event tracepoints for dynamic
 device_node lifecyle
Message-ID: <20180121170140.23d1ff12@gandalf.local.home>
In-Reply-To: <20180121143117.19805-2-wsa+renesas@sang-engineering.com>
References: <20180121143117.19805-1-wsa+renesas@sang-engineering.com>
        <20180121143117.19805-2-wsa+renesas@sang-engineering.com>
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On Sun, 21 Jan 2018 15:31:17 +0100
Wolfram Sang <wsa+renesas@sang-engineering.com> wrote:

> From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
> 
> This patch introduces event tracepoints for tracking a device_nodes
> reference cycle as well as reconfig notifications generated in response
> to node/property manipulations.
> 
> With the recent upstreaming of the refcount API several device_node
> underflows and leaks have come to my attention in the pseries (DLPAR)
> dynamic logical partitioning code (ie. POWER speak for hotplugging
> virtual and physcial resources at runtime such as cpus or IOAs). These
> tracepoints provide a easy and quick mechanism for validating the
> reference counting of device_nodes during their lifetime.
> 
> Further, when pseries lpars are migrated to a different machine we
> perform a live update of our device tree to bring it into alignment with
> the configuration of the new machine. The of_reconfig_notify trace point
> provides a mechanism that can be turned for debuging the device tree
> modifications with out having to build a custom kernel to get at the
> DEBUG code introduced by commit 00aa37206e1a54 ("of/reconfig: Add debug
> output for OF_RECONFIG notifiers").
> 
> The following trace events are provided: of_node_get, of_node_put,
> of_node_release, and of_reconfig_notify. These trace points require a
> kernel built with ftrace support to be enabled. In a typical environment
> where debugfs is mounted at /sys/kernel/debug the entire set of
> tracepoints can be set with the following:
> 
>   echo "of:*" > /sys/kernel/debug/tracing/set_event
> 
> or
> 
>   echo 1 > /sys/kernel/debug/tracing/events/of/enable
> 
> The following shows the trace point data from a DLPAR remove of a cpu
> from a pseries lpar:
> 
> cat /sys/kernel/debug/tracing/trace | grep "POWER8@10"
> 
> cpuhp/23-147   [023] ....   128.324827:
>         of_node_put: refcount=5, dn->full_name=/cpus/PowerPC,POWER8@10
> cpuhp/23-147   [023] ....   128.324829:
>         of_node_put: refcount=4, dn->full_name=/cpus/PowerPC,POWER8@10
> cpuhp/23-147   [023] ....   128.324829:
>         of_node_put: refcount=3, dn->full_name=/cpus/PowerPC,POWER8@10
> cpuhp/23-147   [023] ....   128.324831:
>         of_node_put: refcount=2, dn->full_name=/cpus/PowerPC,POWER8@10
>    drmgr-7284  [009] ....   128.439000:
>         of_node_put: refcount=1, dn->full_name=/cpus/PowerPC,POWER8@10
>    drmgr-7284  [009] ....   128.439002:
>         of_reconfig_notify: action=DETACH_NODE, dn->full_name=/cpus/PowerPC,POWER8@10,
>                             prop->name=null, old_prop->name=null
>    drmgr-7284  [009] ....   128.439015:
>         of_node_put: refcount=0, dn->full_name=/cpus/PowerPC,POWER8@10
>    drmgr-7284  [009] ....   128.439016:
>         of_node_release: dn->full_name=/cpus/PowerPC,POWER8@10, dn->_flags=4
> 
> Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
> [wsa: fixed commit abbrev and one of the sysfs paths in commit desc,
> removed trailing space and fixed pointer declaration in code]
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

From the tracing perspective:

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> ---