From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
Michael Neuling <mikey@neuling.org>,
Gautham R Shenoy <ego@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Mel Gorman <mgorman@techsingularity.net>,
Vincent Guittot <vincent.guittot@linaro.org>,
Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Subject: [PATCH v2 1/2] sched/topology: Allow archs to override cpu_smt_mask
Date: Fri, 7 Aug 2020 13:15:16 +0530 [thread overview]
Message-ID: <20200807074517.27957-1-srikar@linux.vnet.ibm.com> (raw)
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(-)
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);
--
2.18.2
next reply other threads:[~2020-08-07 7:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-07 7:45 Srikar Dronamraju [this message]
2020-08-07 7:45 ` [PATCH v2 2/2] powerpc/topology: Override cpu_smt_mask Srikar Dronamraju
2020-09-17 11:27 ` [PATCH v2 1/2] sched/topology: Allow archs to override cpu_smt_mask Michael Ellerman
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