Re: [RFC][PATCH v2 11/11] perf top: demo of how to use the sysfsinterface

[Lin Ming]

On Thu, 2010-05-20 at 09:33 +0800, Corey Ashford wrote:
> On 5/19/2010 6:17 PM, Lin Ming wrote:
> > On Thu, 2010-05-20 at 02:18 +0800, Corey Ashford wrote:
> >>
> >> On 5/18/2010 6:49 PM, Lin Ming wrote:
> >>> Just a temporary patch to show how to use the pmu sysfs interface...
> >>>
> >>> Signed-off-by: Lin Ming <ming.m.lin@xxxxxxxxx>
> >>> ---
> >>>  tools/perf/builtin-top.c |   13 +++++++++++++
> >>>  1 files changed, 13 insertions(+), 0 deletions(-)
> >>>
> >>> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> >>> index adc179d..eaa9405 100644
> >>> --- a/tools/perf/builtin-top.c
> >>> +++ b/tools/perf/builtin-top.c
> >>> @@ -1206,6 +1206,7 @@ static void start_counter(int i, int counter)
> >>>  	struct perf_event_attr *attr;
> >>>  	int cpu;
> >>>  	int thread_index;
> >>> +	int sys_fd;
> >>>
> >>>  	cpu = profile_cpu;
> >>>  	if (target_tid == -1 && profile_cpu == -1)
> >>> @@ -1226,9 +1227,21 @@ static void start_counter(int i, int counter)
> >>>
> >>>  	for (thread_index = 0; thread_index < thread_num; thread_index++) {
> >>>  try_again:
> >>> +		/*
> >>> +		 * This is just an ugly demo of how to use the sysfs interface.
> >>> +		 * You can also parse the <event-name> and open sys file as,
> >>> +		 * sys_fd = open("/sys/devices/system/cpu/events/<event-name>/event_source/id", O_RDONLY);
> >>> +		 */
> >>
> >> In this above case, does this sys_fd also specify the event I am going to open, in addition to its event source?  I'd assume not since event_source is a symlink to /sys/devices/system/cpu/event_source (right?)
> > 
> > Right, this sys_fd only specifies the event source.
> > 
> >> How do I specify the exact event id via the sysfs interface?
> > 
> > /sys/devices/system/cpu/events/<event-name>/id
> > 
> > But in this patch series, the event id sysfs interface is not used yet.
> 
> So, I would open that id and then read the id code and place it in attr->config or maybe place
> the fd into attr (somewhere) ?

Place the id code in attr->config.

> 
> We also need to take into account event "attributes" - other data that is needed to configure a specific event.  For example, think about a memory controller which has a PMU can count events in a particular memory range; we need to be able to supply the memory range somehow, and I don't think that can be accomplished by passing in the fd of a sysfs file that we've opened.
> 

Each event is a directory in the sysfs, so we can put all the event
"attributes" under it.

For your example,
/sys/devices/system/node/events/<event-name>/id
/sys/devices/system/node/events/<event-name>/memory_range
....

Then we can read these attributes and pass the value into the syscall.

> - Corey
> 

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