linux-kernel - [PATCH v3 3/3] s390x: optimization of the check for CPU topology change

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Date:   Tue,  3 Aug 2021 10:26:46 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, cohuck@...hat.com,
        david@...hat.com, thuth@...hat.com, imbrenda@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, pmorel@...ux.ibm.com
Subject: [PATCH v3 3/3] s390x: optimization of the check for CPU topology change

Now that the PTF instruction is interpreted by the SIE we can optimize
the arch_update_cpu_topology callback to check if there is a real need
to update the topology by using the PTF instruction.

Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
---
 arch/s390/kernel/topology.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c
index 26aa2614ee35..741cb447e78e 100644
--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -322,6 +322,9 @@ int arch_update_cpu_topology(void)
 	struct device *dev;
 	int cpu, rc;
 
+	if (!ptf(PTF_CHECK))
+		return 0;
+
 	rc = __arch_update_cpu_topology();
 	on_each_cpu(__arch_update_dedicated_flag, NULL, 0);
 	for_each_online_cpu(cpu) {
-- 
2.25.1