On 7/6/20 8:43 AM, Michael Ellerman wrote:
Kajol Jain <kj...@linux.ibm.com> writes:
Patch here adds cpu hotplug functions to hv_24x7 pmu.
A new cpuhp_state "CPUHP_AP_PERF_POWERPC_HV_24x7_ONLINE" enum
is added.
The online callback function updates the cpumask only if its
empty. As the primary intention of adding hotplug support
is to designate a CPU to make HCALL to collect the
counter data.
The offline function test and clear corresponding cpu in a cpumask
and update cpumask to any other active cpu.
Signed-off-by: Kajol Jain <kj...@linux.ibm.com>
Reviewed-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
---
arch/powerpc/perf/hv-24x7.c | 45 +++++++++++++++++++++++++++++++++++++
include/linux/cpuhotplug.h | 1 +
2 files changed, 46 insertions(+)
diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index db213eb7cb02..ce4739e2b407 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -31,6 +31,8 @@ static int interface_version;
/* Whether we have to aggregate result data for some domains. */
static bool aggregate_result_elements;
+static cpumask_t hv_24x7_cpumask;
+
static bool domain_is_valid(unsigned domain)
{
switch (domain) {
@@ -1641,6 +1643,44 @@ static struct pmu h_24x7_pmu = {
.capabilities = PERF_PMU_CAP_NO_EXCLUDE,
};
+static int ppc_hv_24x7_cpu_online(unsigned int cpu)
+{
+ /* Make this CPU the designated target for counter collection */
The comment implies every newly onlined CPU will become the target, but
actually it's only the first onlined CPU.
So I think the comment needs updating, or you could just drop the
comment, I think the code is fairly clear by itself.
+ if (cpumask_empty(&hv_24x7_cpumask))
+ cpumask_set_cpu(cpu, &hv_24x7_cpumask);
+
+ return 0;
+}
+
+static int ppc_hv_24x7_cpu_offline(unsigned int cpu)
+{
+ int target = -1;
No need to initialise target, you assign to it unconditionally below.
+ /* Check if exiting cpu is used for collecting 24x7 events */
+ if (!cpumask_test_and_clear_cpu(cpu, &hv_24x7_cpumask))
+ return 0;
+
+ /* Find a new cpu to collect 24x7 events */
+ target = cpumask_last(cpu_active_mask);
Any reason to use cpumask_last() vs cpumask_first(), or a randomly
chosen CPU?
+ if (target < 0 || target >= nr_cpu_ids)
+ return -1;
+
+ /* Migrate 24x7 events to the new target */
+ cpumask_set_cpu(target, &hv_24x7_cpumask);
+ perf_pmu_migrate_context(&h_24x7_pmu, cpu, target);
+
+ return 0;
+}
+
+static int hv_24x7_cpu_hotplug_init(void)
+{
+ return cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_HV_24x7_ONLINE,
+ "perf/powerpc/hv_24x7:online",
+ ppc_hv_24x7_cpu_online,
+ ppc_hv_24x7_cpu_offline);
+}
+
static int hv_24x7_init(void)
{
int r;
@@ -1685,6 +1725,11 @@ static int hv_24x7_init(void)
if (r)
return r;
+ /* init cpuhotplug */
+ r = hv_24x7_cpu_hotplug_init();
+ if (r)
+ pr_err("hv_24x7: CPU hotplug init failed\n");
+
The hotplug initialisation shouldn't fail unless something is badly
wrong. I think you should just fail initialisation of the entire PMU if
that happens, which will make the error handling in the next patch much
simpler.
We did fail the PMU registration on failure of the hotplug
code (and yes error handling is much simpler), but on internal
review/discussion,
what came up was that, hv_24x7 PMU will still be usable without
the hotplug code (with "-C" option to perf tool command line).
Maddy
cheers
r = perf_pmu_register(&h_24x7_pmu, h_24x7_pmu.name, -1);
if (r)
return r;
