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

From: Satheesh Rajendran <[email-masked]>
Date: Wed, 29 Jul 2020 18:24:02 +0530

On Mon, Jul 27, 2020 at 01:25:25PM +0530, Srikar Dronamraju wrote:
> 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/[email-masked]/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.

boot tested on P9 KVM guest.

without this series:
# dmesg|grep smp
[    0.066624] smp: Bringing up secondary CPUs ...
[  347.521264] smp: Brought up 1 node, 2048 CPUs

with this series:
# dmesg|grep smp
[    0.067744] smp: Bringing up secondary CPUs ...
[    5.416910] smp: Brought up 1 node, 2048 CPUs

Tested-by: Satheesh Rajendran <[email-masked]>

Regards,
-Satheesh
> 
> 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 <[email-masked]>
> Cc: LKML <[email-masked]>
> Cc: Michael Ellerman <[email-masked]>
> Cc: Nicholas Piggin <[email-masked]>
> Cc: Anton Blanchard <[email-masked]>
> Cc: Oliver O'Halloran <[email-masked]>
> Cc: Nathan Lynch <[email-masked]>
> Cc: Michael Neuling <[email-masked]>
> Cc: Gautham R Shenoy <[email-masked]>
> Cc: Satheesh Rajendran <[email-masked]>
> Cc: Ingo Molnar <[email-masked]>
> Cc: Peter Zijlstra <[email-masked]>
> Cc: Valentin Schneider <[email-masked]>
> 
> 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
>