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

    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 <sathnaga@linux.vnet.ibm.com>

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

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