| Message ID | 1627979206-32663-4-git-send-email-pmorel@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | s390x: KVM: CPU Topology | expand |
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.
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?
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...
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) {
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(+)