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

From: Pierre Morel <pmorel@linux.ibm.com>
To: kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
	borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com,
	david@redhat.com, thuth@redhat.com, imbrenda@linux.ibm.com,
	hca@linux.ibm.com, gor@linux.ibm.com, pmorel@linux.ibm.com
Subject: [PATCH v3 3/3] s390x: optimization of the check for CPU topology change
Date: Tue,  3 Aug 2021 10:26:46 +0200	[thread overview]
Message-ID: <1627979206-32663-4-git-send-email-pmorel@linux.ibm.com> (raw)
In-Reply-To: <1627979206-32663-1-git-send-email-pmorel@linux.ibm.com>

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@linux.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

