On 10/16/2015 07:54 AM, Michael Ellerman wrote: > On Wed, 2015-10-14 at 15:43 +0530, Anshuman Khandual wrote: >> On 10/14/2015 02:49 PM, Michael Ellerman wrote: >>> On Wed, 2015-10-14 at 14:32 +0530, Anshuman Khandual wrote: >>>> On shared processor LPARs, H_HOME_NODE_ASSOCIATIVITY hcall provides the >>>> dynamic virtual-physical mapping for any given processor. Currently we >>>> use VPHN node ID information only after getting either a PRRN or a VPHN >>>> event. But during boot time inside the function numa_setup_cpu, we still >>>> query the OF device tree for the node ID value which might be different >>>> than what can be fetched from the H_HOME_NODE_ASSOCIATIVITY hcall. In a >>>> scenario where there are no PRRN or VPHN event after boot, all node-cpu >>>> mapping will remain incorrect there after. >>>> >>>> With this proposed change, numa_setup_cpu will try to override the OF >>>> device tree fetched node ID information with H_HOME_NODE_ASSOCIATIVITY >>>> hcall fetched node ID value. Right now shared processor property of the >>>> LPAR cannot be queried as VPA inializaion happens after numa_setup_cpu >>>> during boot time. So initmem_init function has been moved after ppc_md. >>>> setup_arch inside setup_arch during boot. >>> >>> I would be *very* reluctant to change the order of initmem_init() vs >>> setup_arch(). >>> >>> At a minimum you'd need to go through every setup_arch() implementation and >>> carefully determine if the ordering of what it does matters vs >>> initmem_init(). >>> And then you'd need to test on every affected platform. >>> >>> So I suggest you think of a different way to do it if at all possible. >> >> vpa_init() is being called inside pSeries_setup_arch which is ppc_md >> .setup_arch for the platform. Its called directly for the boot cpu >> and through smp_init_pseries_xics for other cpus on the system. Not >> sure what is the reason behind calling vpa_init() from XICS init >> though. >> >> If we can move all these vpa_init() calls from pSeries_setup_arch >> to initmem_init just before calling numa_setup_cpu, the VPA area >> would be initialized when we need it during boot. Will look in >> this direction. > > Back up a bit. The dependency on vpa_init() is only because you want to call > lppaca_shared_proc() right?
Right. > > But do you really need to? What happens if you call VPHN on a non-shared proc > machine? Does it 1) give you something sane or 2) give you an error or 3) give > you a junk value? > > If it's either of 1 or 2 then you should be OK to just call it. You either use > the value it returned which is sane or you see the error and just fall back to > the device tree nid. Most probably it will be a sane value without any error. But the decision to override the DT fetched value will be based on whether we are running on a shared processor LPAR or not. Hence dependency on lppaca_shared_proc(). In case of error from VPHN on a shared processor LPAR, we will still have the DT fetched value to fall back on (will update the logic in the patch for this). _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
