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Date: Thu, 20 May 2010 17:21:29 +0800
From: Lin Ming <ming.m.lin@...el.com>
To: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
Frederic Weisbecker <fweisbec@...il.com>,
Paul Mundt <lethal@...ux-sh.org>,
"eranian@...il.com" <eranian@...il.com>,
"Gary.Mohr@...l.com" <Gary.Mohr@...l.com>,
"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
Paul Mackerras <paulus@...ba.org>,
"David S. Miller" <davem@...emloft.net>,
Russell King <rmk+kernel@....linux.org.uk>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Will Deacon <will.deacon@....com>,
Maynard Johnson <mpjohn@...ibm.com>,
Carl Love <carll@...ibm.com>,
"greg@...ah.com" <greg@...ah.com>,
Kay Sievers <kay.sievers@...y.org>,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH v2 11/11] perf top: demo of how to use the sysfs
interface
On Thu, 2010-05-20 at 16:27 +0800, Corey Ashford wrote:
> On 05/19/2010 07:08 PM, Lin Ming wrote:
> > 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@...el.com>
> >>>>> ---
> >>>>> 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.
> >
>
> I'm not sure I made the example clear.
>
> Let's say I have a memory controller event called memory_write and it
> has two attributes: low_addr and high_addr... writes to addresses
> between the low_addr and high_addr will increment the counter.
>
> As a user, I want to be able to specify a particular memory range, let's
> say 0x1000000..0x2000000
>
> A sysfs structure like this might be constructed:
> /sys/devices/system/node/events/memory_write
> /sys/devices/system/node/events/memory_write/attr
> /sys/devices/system/node/events/memory_write/attr/low_addr
> /sys/devices/system/node/events/memory_write/attr/low_addr/min
> /sys/devices/system/node/events/memory_write/attr/low_addr/max
>
> In another posting I had also added a bit shift value, but there are so
> few bits left in the attr->config, that I'm not sure this is a very
> extensible mechanism, but just for the sake of illustration of the basic
> idea, I'll add it here:
> /sys/devices/system/node/events/memory_write/attr/low_addr/shift
>
> Then the same thing is repeated for the other attribute:
> /sys/devices/system/node/events/memory_write/attr/high_addr
> /sys/devices/system/node/events/memory_write/attr/high_addr/min
> /sys/devices/system/node/events/memory_write/attr/high_addr/max
> /sys/devices/system/node/events/memory_write/attr/high_addr/shift
>
> In this scenario, a user tool (like perf) would be able to see that
> there are attributes associated with the memory_write event, and it
> knows the names and range of allowed values for these attributes. The
> shift value tells the tool how much to shift the attribute value before
> OR'ing it into the attr->config value.
So different events may have different shift value for its attributes.
If an event has 4 attributes, each attribute will have a "shift" in
sysfs, right?
>
> If we find that more than 64 bits are needed for the event code plus the
> attribute values, perhaps shift values greater than 64 would denote to
> place the attribute bits into a new attr field, like
> attr->config_extra[shift / 64]
>
> On the perf command line, then, a user could specify something like:
>
> perf stat -e node::memory_write:low_addr=0x1000000:high_addr=0x2000000
>
> What do you think?
I like your idea.
Thanks,
Lin Ming
>
> - Corey
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