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Re: [kvm-unit-tests PATCH v4 07/12] arm: pmu: Basic event counter Tests


From: Zenghui Yu
Subject: Re: [kvm-unit-tests PATCH v4 07/12] arm: pmu: Basic event counter Tests
Date: Mon, 19 Sep 2022 22:30:01 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

Hi Eric,

A few comments when looking through the PMU test code (2 years after
the series was merged).

On 2020/4/3 15:13, Eric Auger wrote:
Adds the following tests:
- event-counter-config: test event counter configuration
- basic-event-count:
  - programs counters #0 and #1 to count 2 required events
  (resp. CPU_CYCLES and INST_RETIRED). Counter #0 is preset
  to a value close enough to the 32b
  overflow limit so that we check the overflow bit is set
  after the execution of the asm loop.
- mem-access: counts MEM_ACCESS event on counters #0 and #1
  with and without 32-bit overflow.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>

[...]

diff --git a/arm/pmu.c b/arm/pmu.c
index 8c49e50..45dccf7 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -38,6 +43,7 @@
 #define SW_INCR                        0x0
 #define INST_RETIRED           0x8
 #define CPU_CYCLES             0x11
+#define MEM_ACCESS             0x13
 #define INST_PREC              0x1B

The spec spells event 0x001B as INST_SPEC.

 #define STALL_FRONTEND         0x23
 #define STALL_BACKEND          0x24

[...]

@@ -175,6 +188,11 @@ static inline void precise_instrs_loop(int loop, uint32_t 
pmcr)
 }
#define PMCEID1_EL0 sys_reg(3, 3, 9, 12, 7)
+#define PMCNTENSET_EL0 sys_reg(3, 3, 9, 12, 1)
+#define PMCNTENCLR_EL0 sys_reg(3, 3, 9, 12, 2)
+
+#define PMEVTYPER_EXCLUDE_EL1 BIT(31)

Unused macro.

+#define PMEVTYPER_EXCLUDE_EL0 BIT(30)
static bool is_event_supported(uint32_t n, bool warn)
 {
@@ -228,6 +246,224 @@ static void test_event_introspection(void)
        report(required_events, "Check required events are implemented");
 }
+/*
+ * Extra instructions inserted by the compiler would be difficult to compensate
+ * for, so hand assemble everything between, and including, the PMCR accesses
+ * to start and stop counting. isb instructions are inserted to make sure
+ * pmccntr read after this function returns the exact instructions executed
+ * in the controlled block. Loads @loop times the data at @address into x9.
+ */
+static void mem_access_loop(void *addr, int loop, uint32_t pmcr)
+{
+asm volatile(
+       "       msr     pmcr_el0, %[pmcr]\n"
+       "       isb\n"
+       "       mov     x10, %[loop]\n"
+       "1:     sub     x10, x10, #1\n"
+       "       ldr        x9, [%[addr]]\n"
+       "       cmp     x10, #0x0\n"
+       "       b.gt    1b\n"
+       "       msr     pmcr_el0, xzr\n"
+       "       isb\n"
+       :
+       : [addr] "r" (addr), [pmcr] "r" (pmcr), [loop] "r" (loop)
+       : "x9", "x10", "cc");
+}
+
+static void pmu_reset(void)
+{
+       /* reset all counters, counting disabled at PMCR level*/
+       set_pmcr(pmu.pmcr_ro | PMU_PMCR_LC | PMU_PMCR_C | PMU_PMCR_P);
+       /* Disable all counters */
+       write_sysreg_s(ALL_SET, PMCNTENCLR_EL0);
+       /* clear overflow reg */
+       write_sysreg(ALL_SET, pmovsclr_el0);
+       /* disable overflow interrupts on all counters */
+       write_sysreg(ALL_SET, pmintenclr_el1);
+       isb();
+}
+
+static void test_event_counter_config(void)
+{
+       int i;
+
+       if (!pmu.nb_implemented_counters) {
+               report_skip("No event counter, skip ...");
+               return;
+       }
+
+       pmu_reset();
+
+       /*
+        * Test setting through PMESELR/PMXEVTYPER and PMEVTYPERn read,

s/PMESELR/PMSELR/ ?

+        * select counter 0
+        */
+       write_sysreg(1, PMSELR_EL0);
+       /* program this counter to count unsupported event */
+       write_sysreg(0xEA, PMXEVTYPER_EL0);
+       write_sysreg(0xdeadbeef, PMXEVCNTR_EL0);
+       report((read_regn_el0(pmevtyper, 1) & 0xFFF) == 0xEA,
+               "PMESELR/PMXEVTYPER/PMEVTYPERn");

Ditto

+       report((read_regn_el0(pmevcntr, 1) == 0xdeadbeef),
+               "PMESELR/PMXEVCNTR/PMEVCNTRn");

Ditto

+
+       /* try to configure an unsupported event within the range [0x0, 0x3F] */
+       for (i = 0; i <= 0x3F; i++) {
+               if (!is_event_supported(i, false))
+                       break;
+       }
+       if (i > 0x3F) {
+               report_skip("pmevtyper: all events within [0x0, 0x3F] are 
supported");
+               return;
+       }
+
+       /* select counter 0 */
+       write_sysreg(0, PMSELR_EL0);
+       /* program this counter to count unsupported event */

We get the unsupported event number *i* but don't program it into
PMXEVTYPER_EL0 (or PMEVTYPER0_EL0). Is it intentional?

+       write_sysreg(i, PMXEVCNTR_EL0);
+       /* read the counter value */
+       read_sysreg(PMXEVCNTR_EL0);
+       report(read_sysreg(PMXEVCNTR_EL0) == i,
+               "read of a counter programmed with unsupported event");
+
+}

[...]

+
+static void test_mem_access(void)
+{
+       void *addr = malloc(PAGE_SIZE);

*addr* isn't freed at the end of test_mem_access(). The same in
test_chain_promotion() and test_overflow_interrupt().

Zenghui



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