lkml.org 
[lkml]   [2017]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle
From
Date
On 04/18/17 17:07, Frank Rowand wrote:
> On 04/17/17 17:32, Tyrel Datwyler wrote:
>> 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 00aa3720.
>
> I do not like changing individual (or small groups of) printk() style
> debugging information to tracepoint style.
>
> As far as I know, there is no easy way to combine trace data and printk()
> style data to create a single chronology of events. If some of the
> information needed to debug an issue is trace data and some is printk()
> style data then it becomes more difficult to understand the overall
> situation.

And of course the other issue with using tracepoints is the extra space
required to hold the tracepoint info. With the pr_debug() approach, the
space usage can be easily removed for a production kernel via a config
option.

Tracepoints are wonderful technology, but not always the proper tool to
use for debug info.

> If Rob wants to convert printk() style data to trace data (and I can't
> convince him otherwise) then I will have further comments on this specific
> patch.
>
> -Frank
>
>>
>> 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/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>
>> ---
>> drivers/of/dynamic.c | 30 ++++++---------
>> include/trace/events/of.h | 93 +++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 105 insertions(+), 18 deletions(-)
>> create mode 100644 include/trace/events/of.h
>>
>
> < snip >
>
>

\
 
 \ /
  Last update: 2017-04-19 03:43    [W:0.120 / U:7.556 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site