[PATCH 0/7] Optimization to improve cpu online/offline on Powerpc

[Srikar Dronamraju]

Anton reported that his 4096 cpu (1024 cores in a socket) was taking too
long to boot. He also analyzed that most of the time was being spent on
updating cpu_core_mask.

Here are some optimizations and fixes to make ppc64_cpu --smt=8/ppc64_cpu
--smt=1 run faster and hence boot the kernel also faster.

Its based on top of my v4 coregroup support patchset.
http://lore.kernel.org/lkml/20200727053230.19753-1-srikar@linux.vnet.ibm.com/t/#u

The first two patches should solve Anton's immediate problem.
On the unofficial patches, Anton reported that the boot time came from 30
mins to 6 seconds. (Basically a high core count in a single socket
configuration). Satheesh also reported similar numbers.

The rest are simple cleanups/optimizations.

Since cpu_core_mask is an exported symbol for a long duration, lets retain
as a snapshot of cpumask_of_node.

Architecture:        ppc64le
Byte Order:          Little Endian
CPU(s):              160
On-line CPU(s) list: 0-159
Thread(s) per core:  4
Core(s) per socket:  20
Socket(s):           2
NUMA node(s):        2
Model:               2.2 (pvr 004e 1202)
Model name:          POWER9, altivec supported
CPU max MHz:         3800.0000
CPU min MHz:         2166.0000
L1d cache:           32K
L1i cache:           32K
L2 cache:            512K
L3 cache:            10240K
NUMA node0 CPU(s):   0-79
NUMA node8 CPU(s):   80-159

without patch (powerpc/next)
[    0.099347] smp: Bringing up secondary CPUs ...
[    0.832513] smp: Brought up 2 nodes, 160 CPUs

with powerpc/next + coregroup support patchset
[    0.099241] smp: Bringing up secondary CPUs ...
[    0.835627] smp: Brought up 2 nodes, 160 CPUs

with powerpc/next + coregroup + this patchset
[    0.097232] smp: Bringing up secondary CPUs ...
[    0.528457] smp: Brought up 2 nodes, 160 CPUs

x ppc64_cpu --smt=1
+ ppc64_cpu --smt=4

without patch
    N           Min           Max        Median           Avg        Stddev
x 100         11.82         17.06         14.01         14.05     1.2665247
+ 100         12.25         16.59         13.86       14.1143      1.164293

with patch
    N           Min           Max        Median           Avg        Stddev
x 100         12.68         16.15         14.24        14.238    0.75489246
+ 100         12.93         15.85         14.35       14.2897    0.60041813

Cc: linuxppc-dev <linuxppc-dev at lists.ozlabs.org>
Cc: LKML <linux-kernel at vger.kernel.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Nicholas Piggin <npiggin at gmail.com>
Cc: Anton Blanchard <anton at ozlabs.org>
Cc: Oliver O'Halloran <oohall at gmail.com>
Cc: Nathan Lynch <nathanl at linux.ibm.com>
Cc: Michael Neuling <mikey at neuling.org>
Cc: Gautham R Shenoy <ego at linux.vnet.ibm.com>
Cc: Satheesh Rajendran <sathnaga at linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Valentin Schneider <valentin.schneider at arm.com>

Srikar Dronamraju (7):
  powerpc/topology: Update topology_core_cpumask
  powerpc/smp: Stop updating cpu_core_mask
  powerpc/smp: Remove get_physical_package_id
  powerpc/smp: Optimize remove_cpu_from_masks
  powerpc/smp: Limit cpus traversed to within a node.
  powerpc/smp: Stop passing mask to update_mask_by_l2
  powerpc/smp: Depend on cpu_l1_cache_map when adding cpus

 arch/powerpc/include/asm/smp.h      |  5 --
 arch/powerpc/include/asm/topology.h |  7 +--
 arch/powerpc/kernel/smp.c           | 79 +++++++++--------------------
 3 files changed, 24 insertions(+), 67 deletions(-)

-- 
2.17.1