From: Anju T Sudhakar <anju@linux.vnet.ibm.com>
To: mpe@ellerman.id.au
Cc: aravinda@linux.vnet.ibm.com, maddy@linux.vnet.ibm.com,
linuxppc-dev@lists.ozlabs.org, anju@linux.vnet.ibm.com,
ego@linux.vnet.ibm.com
Subject: [PATCH] powerpc/perf: Use cpumask_last() to determine the
Date: Mon, 20 May 2019 14:35:01 +0530 [thread overview]
Message-ID: <20190520090501.20415-1-anju@linux.vnet.ibm.com> (raw)
Nest and core imc(In-memory Collection counters) assigns a particular
cpu as the designated target for counter data collection.
During system boot, the first online cpu in a chip gets assigned as
the designated cpu for that chip(for nest-imc) and the first online cpu
in a core gets assigned as the designated cpu for that core(for core-imc).
If the designated cpu goes offline, the next online cpu from the same
chip(for nest-imc)/core(for core-imc) is assigned as the next target,
and the event context is migrated to the target cpu.
Currently, cpumask_any_but() function is used to find the target cpu.
Though this function is expected to return a `random` cpu, this always
returns the next online cpu.
If all cpus in a chip/core is offlined in a sequential manner, starting
from the first cpu, the event migration has to happen for all the cpus
which goes offline. Since the migration process involves a grace period,
the total time taken to offline all the cpus will be significantly high.
Example:
In a system which has 2 sockets, with
NUMA node0 CPU(s): 0-87
NUMA node8 CPU(s): 88-175
Time taken to offline cpu 88-175:
real 2m56.099s
user 0m0.191s
sys 0m0.000s
Use cpumask_last() to choose the target cpu, when the designated cpu
goes online, so the migration will happen only when the last_cpu in the
mask goes offline. This way the time taken to offline all cpus in a
chip/core can be reduced.
With the patch,
Time taken to offline cpu 88-175:
real 0m12.207s
user 0m0.171s
sys 0m0.000s
cpumask_last() is a better way to find the target cpu, since in most of the
cases cpuhotplug is performed in an increasing order(even in ppc64_cpu).
cpumask_any_but() can still be used to check the possibility of other
online cpus from the same chip/core if the last cpu in the mask goes
offline.
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
---
arch/powerpc/perf/imc-pmu.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 31fa753..fbfd6e7 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -366,7 +366,14 @@ static int ppc_nest_imc_cpu_offline(unsigned int cpu)
*/
nid = cpu_to_node(cpu);
l_cpumask = cpumask_of_node(nid);
- target = cpumask_any_but(l_cpumask, cpu);
+ target = cpumask_last(l_cpumask);
+
+ /*
+ * If this(target) is the last cpu in the cpumask for this chip,
+ * check for any possible online cpu in the chip.
+ */
+ if (unlikely(target == cpu))
+ target = cpumask_any_but(l_cpumask, cpu);
/*
* Update the cpumask with the target cpu and
@@ -671,7 +678,10 @@ static int ppc_core_imc_cpu_offline(unsigned int cpu)
return 0;
/* Find any online cpu in that core except the current "cpu" */
- ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu);
+ ncpu = cpumask_last(cpu_sibling_mask(cpu));
+
+ if (unlikely(ncpu == cpu))
+ ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu);
if (ncpu >= 0 && ncpu < nr_cpu_ids) {
cpumask_set_cpu(ncpu, &core_imc_cpumask);
--
1.8.3.1
next reply other threads:[~2019-05-20 9:07 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 9:05 Anju T Sudhakar [this message]
2019-05-20 9:22 ` [PATCH] powerpc/perf: Use cpumask_last() to determine the Anju T Sudhakar
2019-05-21 5:14 ` Madhavan Srinivasan
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