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Tue, 3 Aug 2021 08:42:39 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 13D53A405C; Tue, 3 Aug 2021 08:42:39 +0000 (GMT) Received: from osiris (unknown [9.145.48.2]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Tue, 3 Aug 2021 08:42:39 +0000 (GMT) Date: Tue, 3 Aug 2021 10:42:37 +0200 From: Heiko Carstens To: Pierre Morel Cc: kvm@vger.kernel.org, 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, gor@linux.ibm.com Subject: Re: [PATCH v3 3/3] s390x: optimization of the check for CPU topology change Message-ID: References: <1627979206-32663-1-git-send-email-pmorel@linux.ibm.com> <1627979206-32663-4-git-send-email-pmorel@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1627979206-32663-4-git-send-email-pmorel@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: _zBAYTduUOhsfzH8ZF1Yxt6t7wWKx4R4 X-Proofpoint-GUID: 65WDoWgONNZ_myn3wcbaz-9JspD4ZldW X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-03_02:2021-08-03,2021-08-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 mlxscore=0 bulkscore=0 phishscore=0 malwarescore=0 clxscore=1015 priorityscore=1501 adultscore=0 impostorscore=0 lowpriorityscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108030059 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 03, 2021 at 10:26:46AM +0200, Pierre Morel wrote: > 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 > --- > 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; > + We have a timer which checks if topology changed and then triggers a call to arch_update_cpu_topology() via rebuild_sched_domains(). With this change topology changes would get lost.