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Srikar Dronamraju e91077cf17 powerpc/smp: Update cpu_core_map on all PowerPc systems 
[ Upstream commit b8b928030332a0ca16d42433eb2c3085600d8704 ]

lscpu() uses core_siblings to list the number of sockets in the
system. core_siblings is set using topology_core_cpumask.

While optimizing the powerpc bootup path, Commit 4ca234a9cb
("powerpc/smp: Stop updating cpu_core_mask").  it was found that
updating cpu_core_mask() ended up taking a lot of time. It was thought
that on Powerpc, cpu_core_mask() would always be same as
cpu_cpu_mask() i.e number of sockets will always be equal to number of
nodes. As an optimization, cpu_core_mask() was made a snapshot of
cpu_cpu_mask().

However that was found to be false with PowerPc KVM guests, where each
node could have more than one socket. So with Commit c47f892d7aa6
("powerpc/smp: Reintroduce cpu_core_mask"), cpu_core_mask was updated
based on chip_id but in an optimized way using some mask manipulations
and chip_id caching.

However on non-PowerNV and non-pseries KVM guests (i.e not
implementing cpu_to_chip_id(), continued to use a copy of
cpu_cpu_mask().

There are two issues that were noticed on such systems
1. lscpu would report one extra socket.
On a IBM,9009-42A (aka zz system) which has only 2 chips/ sockets/
nodes, lscpu would report
Architecture:        ppc64le
Byte Order:          Little Endian
CPU(s):              160
On-line CPU(s) list: 0-159
Thread(s) per core:  8
Core(s) per socket:  6
Socket(s):           3                <--------------
NUMA node(s):        2
Model:               2.2 (pvr 004e 0202)
Model name:          POWER9 (architected), altivec supported
Hypervisor vendor:   pHyp
Virtualization type: para
L1d cache:           32K
L1i cache:           32K
L2 cache:            512K
L3 cache:            10240K
NUMA node0 CPU(s):   0-79
NUMA node1 CPU(s):   80-159

2. Currently cpu_cpu_mask is updated when a core is
added/removed. However its not updated when smt mode switching or on
CPUs are explicitly offlined. However all other percpu masks are
updated to ensure only active/online CPUs are in the masks.
This results in build_sched_domain traces since there will be CPUs in
cpu_cpu_mask() but those CPUs are not present in SMT / CACHE / MC /
NUMA domains. A loop of threads running smt mode switching and core
add/remove will soon show this trace.
Hence cpu_cpu_mask has to be update at smt mode switch.

This will have impact on cpu_core_mask(). cpu_core_mask() is a
snapshot of cpu_cpu_mask. Different CPUs within the same socket will
end up having different cpu_core_masks since they are snapshots at
different points of time. This means when lscpu will start reporting
many more sockets than the actual number of sockets/ nodes / chips.

Different ways to handle this problem:
A. Update the snapshot aka cpu_core_mask for all CPUs whenever
   cpu_cpu_mask is updated. This would a non-optimal solution.
B. Instead of a cpumask_var_t, make cpu_core_map a cpumask pointer
   pointing to cpu_cpu_mask. However percpu cpumask pointer is frowned
   upon and we need a clean way to handle PowerPc KVM guest which is
   not a snapshot.
C. Update cpu_core_masks all PowerPc systems like in PowerPc KVM
guests using mask manipulations. This approach is relatively simple
and unifies with the existing code.
D. On top of 3, we could also resurrect get_physical_package_id which
   could return a nid for the said CPU. However this is not needed at this
   time.

Option C is the preferred approach for now.

While this is somewhat a revert of Commit 4ca234a9cb ("powerpc/smp:
Stop updating cpu_core_mask").

1. Plain revert has some conflicts
2. For chip_id == -1, the cpu_core_mask is made identical to
cpu_cpu_mask, unlike previously where cpu_core_mask was set to a core
if chip_id doesn't exist.

This goes by the principle that if chip_id is not exposed, then
sockets / chip / node share the same set of CPUs.

With the fix, lscpu o/p would be
Architecture:        ppc64le
Byte Order:          Little Endian
CPU(s):              160
On-line CPU(s) list: 0-159
Thread(s) per core:  8
Core(s) per socket:  6
Socket(s):           2                     <--------------
NUMA node(s):        2
Model:               2.2 (pvr 004e 0202)
Model name:          POWER9 (architected), altivec supported
Hypervisor vendor:   pHyp
Virtualization type: para
L1d cache:           32K
L1i cache:           32K
L2 cache:            512K
L3 cache:            10240K
NUMA node0 CPU(s):   0-79
NUMA node1 CPU(s):   80-159

Fixes: 4ca234a9cb ("powerpc/smp: Stop updating cpu_core_mask")
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210826100401.412519-3-srikar@linux.vnet.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-09-18 13:40:15 +02:00
arch powerpc/smp: Update cpu_core_map on all PowerPc systems 2021-09-18 13:40:15 +02:00
block scsi: bsg: Remove support for SCSI_IOCTL_SEND_COMMAND 2021-09-18 13:40:11 +02:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-15 09:50:29 +02:00
crypto crypto: sm2 - fix a memory leak in sm2 2021-07-14 16:56:06 +02:00
Documentation docs: Fix infiniband uverbs minor number 2021-09-18 13:40:11 +02:00
drivers platform/x86: dell-smbios-wmi: Add missing kfree in error-exit from run_smbios_call 2021-09-18 13:40:15 +02:00
fs NFSv4/pnfs: The layout barrier indicate a minimal value for the seqid 2021-09-18 13:40:13 +02:00
include iommu/vt-d: Update the virtual command related registers 2021-09-18 13:40:14 +02:00
init sched/core: Initialize the idle task with preemption disabled 2021-07-14 16:55:50 +02:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-26 12:06:54 +02:00
kernel dma-debug: fix debugfs initialization order 2021-09-18 13:40:13 +02:00
lib lib/mpi: use kcalloc in mpi_resize 2021-09-15 09:50:29 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/page_alloc: speed up the iteration of max_order 2021-09-12 08:58:26 +02:00
net sunrpc: Fix return value of get_srcport() 2021-09-18 13:40:14 +02:00
samples samples: pktgen: add missing IPv6 option to pktgen scripts 2021-09-15 09:50:40 +02:00
scripts scripts/tracing: fix the bug that can't parse raw_trace_func 2021-08-12 13:22:12 +02:00
security IMA: remove the dependency on CRYPTO_MD5 2021-09-15 09:50:48 +02:00
sound ASoC: rt5682: Remove unused variable in rt5682_i2c_remove() 2021-09-15 09:50:46 +02:00
tools tools/thermal/tmon: Add cross compiling support 2021-09-18 13:40:07 +02:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: Do not leak memory for duplicate debugfs directories 2021-08-12 13:22:17 +02:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS f2fs: move ioctl interface definitions to separated file 2021-05-19 10:13:00 +02:00
Makefile Linux 5.10.66 2021-09-16 12:51:23 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.