Messages in this thread | | | Subject | Re: [PATCH v3 3/3] s390x: optimization of the check for CPU topology change | From | Pierre Morel <> | Date | Tue, 3 Aug 2021 11:28:56 +0200 |
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On 8/3/21 10:57 AM, Pierre Morel wrote: > > > On 8/3/21 10:42 AM, Heiko Carstens wrote: >> 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 <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; >>> + >> >> 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. > > For my understanding, if PTF check return 0 it means that there are no > topology changes. > So they could not get lost. > > What did I miss? > > I missed that PTF clears the MCTR... and only one of the two calls will return 1 while we need both to return 1...
-- Pierre Morel IBM Lab Boeblingen
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