Re: [PATCH v2 5/5] arm64: perf: Add support for chaining event counters

From: Suzuki K Poulose
Date: Mon Jun 11 2018 - 12:19:05 EST

On 11/06/18 15:24, Mark Rutland wrote:
On Mon, Jun 11, 2018 at 02:54:16PM +0100, Suzuki K Poulose wrote:
On 08/06/18 15:46, Suzuki K Poulose wrote:
On 06/06/2018 07:01 PM, Mark Rutland wrote:
On Tue, May 29, 2018 at 11:55:56AM +0100, Suzuki K Poulose wrote:

-ÂÂÂÂÂÂÂ value |= 0xffffffff00000000ULL;
+ÂÂÂÂÂÂÂ if (!armv8pmu_event_is_64bit(event))
+ÂÂÂÂÂÂÂÂÂÂÂ value |= 0xffffffff00000000ULL;
ÂÂÂÂÂÂÂÂÂ write_sysreg(value, pmccntr_el0);
-ÂÂÂ } else if (armv8pmu_select_counter(idx) == idx)
-ÂÂÂÂÂÂÂ write_sysreg(value, pmxevcntr_el0);
+ÂÂÂ } else
+ÂÂÂÂÂÂÂ armv8pmu_write_hw_counter(event, value);

+static inline void armv8pmu_write_event_type(struct perf_event *event)
+ÂÂÂ struct hw_perf_event *hwc = &event->hw;
+ÂÂÂ int idx = hwc->idx;
+ÂÂÂ /*
+ÂÂÂÂ * For chained events, write the the low counter event type
+ÂÂÂÂ * followed by the high counter. The high counter is programmed
+ÂÂÂÂ * with CHAIN event code with filters set to count at all ELs.
+ÂÂÂÂ */
+ÂÂÂ if (armv8pmu_event_is_chained(event)) {
+ÂÂÂÂÂÂÂ armv8pmu_write_evtype(idx - 1, hwc->config_base);
+ÂÂÂÂÂÂÂ isb();
+ÂÂÂÂÂÂÂ armv8pmu_write_evtype(idx, chain_evt);

The ISB isn't necessary here, AFAICT. We only do this while the PMU is
disabled; no?

You're right. I was just following the ARM ARM.

Taking another look, it is not clear about the semantics of "pmu->enable()"
and pmu->disable() callbacks.

I was talking about pmu::{pmu_disable,pmu_enable}(), so I'm not sure I
follow how arm_pmu::{enable,disable}() are relevant here.> The arm_pmu::{enable,disable}() callbacks enable or disable individual
counters. For example, leaving unused counters disabled may save power,
even if the PMU as a whole is enabled.

Ah, I mistook cpu_pmu->enable/disable for the core pmu ops. My bad.
Sorry about the noise.