Re: [RFC PATCH v9 5/7] perf: cavium: Support memory controller PMU counters

Jan Glauber
2017-08-31T15:27:38Z

On Thu, Aug 31, 2017 at 02:26:22PM +0100, Suzuki K Poulose wrote:
> On 31/08/17 12:35, Jan Glauber wrote:
> >On Wed, Aug 30, 2017 at 11:03:00AM +0100, Suzuki K Poulose wrote:
> >>On 29/08/17 14:12, Jan Glauber wrote:

[...]

> >>>+/* LMC events */
> >>>+#define LMC_EVENT_IFB_CNT 0x1d0
> >>>+#define LMC_EVENT_OPS_CNT 0x1d8
> >>>+#define LMC_EVENT_DCLK_CNT 0x1e0
> >>>+#define LMC_EVENT_BANK_CONFLICT1 0x360
> >>>+#define LMC_EVENT_BANK_CONFLICT2 0x368
> >>>+
> >>>+#define CVM_PMU_LMC_EVENT_ATTR(_name, _id) \
> >>>+ &((struct perf_pmu_events_attr[]) { \
> >>>+ { \
> >>>+ __ATTR(_name, S_IRUGO, cvm_pmu_event_sysfs_show, NULL), \
> >>>+ _id, \
> >>>+ "lmc_event=" __stringify(_id), \
> >>>+ } \
> >>>+ })[0].attr.attr
> >>>+
> >>>+/* map counter numbers to register offsets */
> >>>+static int lmc_events[] = {
> >>>+ LMC_EVENT_IFB_CNT,
> >>>+ LMC_EVENT_OPS_CNT,
> >>>+ LMC_EVENT_DCLK_CNT,
> >>>+ LMC_EVENT_BANK_CONFLICT1,
> >>>+ LMC_EVENT_BANK_CONFLICT2,
> >>>+};
> >>>+
> >>>+static int cvm_pmu_lmc_add(struct perf_event *event, int flags)
> >>>+{
> >>>+ struct hw_perf_event *hwc = &event->hw;
> >>>+
> >>>+ return cvm_pmu_add(event, flags, LMC_CONFIG_OFFSET,
> >>>+ lmc_events[hwc->config]);
> >>>+}
> >>>+
> >>
> >>Is there any reason why we can't use the LMC event code directly
> >>here, avoiding the mapping altogether ?
> >
> >I wanted to avoid exposing the raw numbers (0x1d0 - 0x368) here.
>
> Thats the primarily the reason why we expose the "aliases" in events/.
> The other problem with adding another layer of mapping is, you are preventing
> someone from actually mapping the raw code used by the perf tool (which is now
> a mapping index) to the real raw code used by the hardware unless they have
> the kernel source handy. If you choose to expose the raw numbers, like *all*
> the other PMUs, the user can map it by looking up the manual.

So what would that do to the config bits? Currently they are:
PMU_FORMAT_ATTR(lmc_event, "config:0-2");

Should I have config:0-9 then? Wouldn't that be confusing as there are
only 5 events?

Also I need to be very careful as we need to prevent a user from
accessing anything else then the counters. I can do that with the
event_valid callback though.

thanks,
Jan

> Cheers
> Suzuki