Re: [PATCH 1/1] powerpc/smp: Set numa node before updating mask

From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Scott Cheloha <cheloha@linux.ibm.com>,
	Geetika Moolchandani <Geetika.Moolchandani1@ibm.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Laurent Dufour <ldufour@linux.vnet.ibm.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 1/1] powerpc/smp: Set numa node before updating mask
Date: Wed, 7 Apr 2021 22:19:30 +0530	[thread overview]
Message-ID: <20210407164930.GJ2339179@linux.vnet.ibm.com> (raw)
In-Reply-To: <87eefml22p.fsf@linux.ibm.com>

* Nathan Lynch <nathanl@linux.ibm.com> [2021-04-07 07:19:10]:

> Sorry for the delay in following up here.
> 

No issues.

> >> So I'd suggest that pseries_add_processor() be made to update
> >> these things when the CPUs are marked present, before onlining them.
> >
> > In pseries_add_processor, we are only marking the cpu as present. i.e
> > I believe numa_setup_cpu() would not have been called. So we may not have a
> > way to associate the CPU to the node. Otherwise we will have to call
> > numa_setup_cpu() or the hcall_vphn.
> >
> > We could try calling numa_setup_cpu() immediately after we set the
> > CPU to be present, but that would be one more extra hcall + I dont know if
> > there are any more steps needed before CPU being made present and
> > associating the CPU to the node.
> 
> An additional hcall in this path doesn't seem too expensive.
> 
> > Are we sure the node is already online?
> 
> I see that dlpar_online_cpu() calls find_and_online_cpu_nid(), so yes I
> think that's covered.

Okay, 

Can we just call set_cpu_numa_node() at the end of map_cpu_to_node().
The advantage would be the update to numa_cpu_lookup_table and cpu_to_node
would happen at the same time and would be in sync.

-- 
Thanks and Regards
Srikar Dronamraju