| Message ID | 20200807074517.27957-1-srikar@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3babbe447d76ac2919ec4d0eb3b0adfb22f5b03c |
| Headers | show |
| Series | [v2,1/2] sched/topology: Allow archs to override cpu_smt_mask | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (3cd2184115b85cc8242fec3d42529cd112962984) |
| snowpatch_ozlabs/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 8 lines checked |
| snowpatch_ozlabs/needsstable | success | Patch has no Fixes tags |
On Fri, 7 Aug 2020 13:15:16 +0530, Srikar Dronamraju wrote: > cpu_smt_mask tracks topology_sibling_cpumask. This would be good for > most architectures. One of the users of cpu_smt_mask(), would be to > identify idle-cores. On Power9, a pair of SMT4 cores can be presented by > the firmware as a SMT8 core for backward compatibility reasons. > > Powerpc allows LPARs to be live migrated from Power8 to Power9. Do note > Power8 had only SMT8 cores. Existing software which has been > developed/configured for Power8 would expect to see SMT8 core. > Maintaining the illusion of SMT8 core is a requirement to make that > work. > > [...] Applied to powerpc/next. [1/2] sched/topology: Allow archs to override cpu_smt_mask https://git.kernel.org/powerpc/c/3babbe447d76ac2919ec4d0eb3b0adfb22f5b03c [2/2] powerpc/topology: Override cpu_smt_mask https://git.kernel.org/powerpc/c/f3232321db58480804f80d59aeb651a5c859a200 cheers
diff --git a/include/linux/topology.h b/include/linux/topology.h index 608fa4aadf0e..ad03df1cc266 100644 --- a/include/linux/topology.h +++ b/include/linux/topology.h @@ -198,7 +198,7 @@ static inline int cpu_to_mem(int cpu) #define topology_die_cpumask(cpu) cpumask_of(cpu) #endif -#ifdef CONFIG_SCHED_SMT +#if defined(CONFIG_SCHED_SMT) && !defined(cpu_smt_mask) static inline const struct cpumask *cpu_smt_mask(int cpu) { return topology_sibling_cpumask(cpu);
cpu_smt_mask tracks topology_sibling_cpumask. This would be good for most architectures. One of the users of cpu_smt_mask(), would be to identify idle-cores. On Power9, a pair of SMT4 cores can be presented by the firmware as a SMT8 core for backward compatibility reasons. Powerpc allows LPARs to be live migrated from Power8 to Power9. Do note Power8 had only SMT8 cores. Existing software which has been developed/configured for Power8 would expect to see SMT8 core. Maintaining the illusion of SMT8 core is a requirement to make that work. In order to maintain above userspace backward compatibility with previous versions of processor, Power9 onwards there is option to the firmware to advertise a pair of SMT4 cores as a fused cores aka SMT8 core. On Power9 this pair shares the L2 cache as well. However, from the scheduler's point of view, a core should be determined by SMT4, since its a completely independent unit of compute. Hence allow PowerPc architecture to override the default cpu_smt_mask() to point to the SMT4 cores in a SMT8 mode. This will ensure the scheduler is always given the right information. Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org> Cc: LKML <linux-kernel@vger.kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michael Neuling <mikey@neuling.org> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Vaidyanathan Srinivasan <svaidy@linux.ibm.com> Acked-by; Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- Changelog v1->v2: Update the commit msg based on the discussion in community esp with Peter Zijlstra and Michael Ellerman. include/linux/topology.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)