powerpc/64s: Implement PMU override command line option

It can be useful in simulators (with very constrained environments)
to allow some PMCs to run from boot so they can be sampled directly
by a test harness, rather than having to run perf.

A previous change freezes counters at boot by default, so provide
a boot time option to un-freeze (plus a bit more flexibility).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-13-npiggin@gmail.com

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9725c546a0d46db7eda7b138f34511af5558d453..2711ddb4835ac36491d257582959ca2e99e78ff4 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4144,6 +4144,14 @@
                        Override pmtimer IOPort with a hex value.
                        e.g. pmtmr=0x508
 
+       pmu_override=   [PPC] Override the PMU.
+                       This option takes over the PMU facility, so it is no
+                       longer usable by perf. Setting this option starts the
+                       PMU counters by setting MMCR0 to 0 (the FC bit is
+                       cleared). If a number is given, then MMCR1 is set to
+                       that number, otherwise (e.g., 'pmu_override=on'), MMCR1
+                       remains 0.
+
        pm_debug_messages       [SUSPEND,KNL]
                        Enable suspend/resume debug messages during boot up.
 

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 73e62e9b179bc9e7bfa671ad723be1f2bd733a58..8d4ff93462fbb2b81750ae7969ba19ceb7a96b2b 100644 (file)
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2419,8 +2419,24 @@ int register_power_pmu(struct power_pmu *pmu)
 }
 
 #ifdef CONFIG_PPC64
+static bool pmu_override = false;
+static unsigned long pmu_override_val;
+static void do_pmu_override(void *data)
+{
+       ppc_set_pmu_inuse(1);
+       if (pmu_override_val)
+               mtspr(SPRN_MMCR1, pmu_override_val);
+       mtspr(SPRN_MMCR0, mfspr(SPRN_MMCR0) & ~MMCR0_FC);
+}
+
 static int __init init_ppc64_pmu(void)
 {
+       if (cpu_has_feature(CPU_FTR_HVMODE) && pmu_override) {
+               pr_warn("disabling perf due to pmu_override= command line option.\n");
+               on_each_cpu(do_pmu_override, NULL, 1);
+               return 0;
+       }
+
        /* run through all the pmu drivers one at a time */
        if (!init_power5_pmu())
                return 0;
@@ -2442,4 +2458,23 @@ static int __init init_ppc64_pmu(void)
                return init_generic_compat_pmu();
 }
 early_initcall(init_ppc64_pmu);
+
+static int __init pmu_setup(char *str)
+{
+       unsigned long val;
+
+       if (!early_cpu_has_feature(CPU_FTR_HVMODE))
+               return 0;
+
+       pmu_override = true;
+
+       if (kstrtoul(str, 0, &val))
+               val = 0;
+
+       pmu_override_val = val;
+
+       return 1;
+}
+__setup("pmu_override=", pmu_setup);
+
 #endif