Messages in this thread | | | Date | Tue, 18 Apr 2023 22:55:25 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH 1/2] pseries/smp: export the smt level in the SYS FS. |
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* Laurent Dufour <ldufour@linux.ibm.com> [2023-04-13 17:38:51]:
> On 13/04/2023 15:37:59, Michael Ellerman wrote: > > Hi Laurent, > > > > Laurent Dufour <ldufour@linux.ibm.com> writes: > >> There is no SMT level recorded in the kernel neither in user space. > >> Indeed there is no real constraint about that and mixed SMT levels are > >> allowed and system is working fine this way. > >> > >> However when new CPU are added, the kernel is onlining all the threads > >> which is leading to mixed SMT levels and confuse end user a bit. > >> > >> To prevent this exports a SMT level from the kernel so user space > >> application like the energy daemon, could read it to adjust their settings. > >> There is no action unless recording the value when a SMT value is written > >> into the new sysfs entry. User space applications like ppc64_cpu should > >> update the sysfs when changing the SMT level to keep the system consistent. > >> > >> Suggested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> > >> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > >> --- > >> arch/powerpc/platforms/pseries/pseries.h | 3 ++ > >> arch/powerpc/platforms/pseries/smp.c | 39 ++++++++++++++++++++++++ > >> 2 files changed, 42 insertions(+) > > > > There is a generic sysfs interface for smt in /sys/devices/system/cpu/smt > > > > I think we should be enabling that on powerpc and then adapting it to > > our needs, rather than adding a pseries specific file. > > Thanks Michael, I was not aware of this sysfs interface. > > > Currently the generic code is only aware of SMT on/off, so it would need > > to be taught about SMT4 and 8 at least. > > Do you think we should limit our support to SMT4 and SMT8 only?
smt2 is also a valid already supported configuration and we are evaluating smt6 mode based on some inputs from ISV teams.
So I believe having a value for all modes would be good.
> > > There are already hooks in the generic code to check the SMT level when > > bringing CPUs up, see cpu_smt_allowed(), they may work for the pseries > > hotplug case too, though maybe we need some additional logic. > > > > Wiring up the basic support is pretty straight forward, something like > > the diff below. >
-- Thanks and Regards Srikar Dronamraju
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