linux-stable.git/kernel/sched/fair.c, branch v6.4

Merge tag 'sched-core-2023-04-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2023-04-28T21:53:30+00:00

Pull scheduler updates from Ingo Molnar:

 - Allow unprivileged PSI poll()ing

 - Fix performance regression introduced by mm_cid

 - Improve livepatch stalls by adding livepatch task switching to
   cond_resched(). This resolves livepatching busy-loop stalls with
   certain CPU-bound kthreads

 - Improve sched_move_task() performance on autogroup configs

 - On core-scheduling CPUs, avoid selecting throttled tasks to run

 - Misc cleanups, fixes and improvements

* tag 'sched-core-2023-04-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/clock: Fix local_clock() before sched_clock_init()
  sched/rt: Fix bad task migration for rt tasks
  sched: Fix performance regression introduced by mm_cid
  sched/core: Make sched_dynamic_mutex static
  sched/psi: Allow unprivileged polling of N*2s period
  sched/psi: Extract update_triggers side effect
  sched/psi: Rename existing poll members in preparation
  sched/psi: Rearrange polling code in preparation
  sched/fair: Fix inaccurate tally of ttwu_move_affine
  vhost: Fix livepatch timeouts in vhost_worker()
  livepatch,sched: Add livepatch task switching to cond_resched()
  livepatch: Skip task_call_func() for current task
  livepatch: Convert stack entries array to percpu
  sched: Interleave cfs bandwidth timers for improved single thread performance at low utilization
  sched/core: Reduce cost of sched_move_task when config autogroup
  sched/core: Avoid selecting the task that is throttled to run when core-sched enable
  sched/topology: Make sched_energy_mutex,update static

Merge tag 'mm-stable-2023-04-27-15-30' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2023-04-28T02:42:02+00:00

Pull MM updates from Andrew Morton:

- Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of
switching from a user process to a kernel thread.

- More folio conversions from Kefeng Wang, Zhang Peng and Pankaj
Raghav.

- zsmalloc performance improvements from Sergey Senozhatsky.

- Yue Zhao has found and fixed some data race issues around the
alteration of memcg userspace tunables.

- VFS rationalizations from Christoph Hellwig:
- removal of most of the callers of write_one_page()
- make __filemap_get_folio()'s return value more useful

- Luis Chamberlain has changed tmpfs so it no longer requires swap
backing. Use `mount -o noswap'.

- Qi Zheng has made the slab shrinkers operate locklessly, providing
some scalability benefits.

- Keith Busch has improved dmapool's performance, making part of its
operations O(1) rather than O(n).

- Peter Xu adds the UFFD_FEATURE_WP_UNPOPULATED feature to userfaultd,
permitting userspace to wr-protect anon memory unpopulated ptes.

- Kirill Shutemov has changed MAX_ORDER's meaning to be inclusive
rather than exclusive, and has fixed a bunch of errors which were
caused by its unintuitive meaning.

- Axel Rasmussen give userfaultfd the UFFDIO_CONTINUE_MODE_WP feature,
which causes minor faults to install a write-protected pte.

- Vlastimil Babka has done some maintenance work on vma_merge():
cleanups to the kernel code and improvements to our userspace test
harness.

- Cleanups to do_fault_around() by Lorenzo Stoakes.

- Mike Rapoport has moved a lot of initialization code out of various
mm/ files and into mm/mm_init.c.

- Lorenzo Stoakes removd vmf_insert_mixed_prot(), which was added for
DRM, but DRM doesn't use it any more.

- Lorenzo has also coverted read_kcore() and vread() to use iterators
and has thereby removed the use of bounce buffers in some cases.

- Lorenzo has also contributed further cleanups of vma_merge().

- Chaitanya Prakash provides some fixes to the mmap selftesting code.

- Matthew Wilcox changes xfs and afs so they no longer take sleeping
locks in ->map_page(), a step towards RCUification of pagefaults.

- Suren Baghdasaryan has improved mmap_lock scalability by switching to
per-VMA locking.

- Frederic Weisbecker has reworked the percpu cache draining so that it
no longer causes latency glitches on cpu isolated workloads.

- Mike Rapoport cleans up and corrects the ARCH_FORCE_MAX_ORDER Kconfig
logic.

- Liu Shixin has changed zswap's initialization so we no longer waste a
chunk of memory if zswap is not being used.

- Yosry Ahmed has improved the performance of memcg statistics
flushing.

- David Stevens has fixed several issues involving khugepaged,
userfaultfd and shmem.

- Christoph Hellwig has provided some cleanup work to zram's IO-related
code paths.

- David Hildenbrand has fixed up some issues in the selftest code's
testing of our pte state changing.

- Pankaj Raghav has made page_endio() unneeded and has removed it.

- Peter Xu contributed some rationalizations of the userfaultfd
selftests.

- Yosry Ahmed has fixed an issue around memcg's page recalim
accounting.

- Chaitanya Prakash has fixed some arm-related issues in the
selftests/mm code.

- Longlong Xia has improved the way in which KSM handles hwpoisoned
pages.

- Peter Xu fixes a few issues with uffd-wp at fork() time.

- Stefan Roesch has changed KSM so that it may now be used on a
per-process and per-cgroup basis.

* tag 'mm-stable-2023-04-27-15-30' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (369 commits)
mm,unmap: avoid flushing TLB in batch if PTE is inaccessible
shmem: restrict noswap option to initial user namespace
mm/khugepaged: fix conflicting mods to collapse_file()
sparse: remove unnecessary 0 values from rc
mm: move 'mmap_min_addr' logic from callers into vm_unmapped_area()
hugetlb: pte_alloc_huge() to replace huge pte_alloc_map()
maple_tree: fix allocation in mas_sparse_area()
mm: do not increment pgfault stats when page fault handler retries
zsmalloc: allow only one active pool compaction context
selftests/mm: add new selftests for KSM
mm: add new KSM process and sysfs knobs
mm: add new api to enable ksm per process
mm: shrinkers: fix debugfs file permissions
mm: don't check VMA write permissions if the PTE/PMD indicates write permissions
migrate_pages_batch: fix statistics for longterm pin retry
userfaultfd: use helper function range_in_vma()
lib/show_mem.c: use for_each_populated_zone() simplify code
mm: correct arg in reclaim_pages()/reclaim_clean_pages_from_list()
fs/buffer: convert create_page_buffers to folio_create_buffers
fs/buffer: add folio_create_empty_buffers helper
...

Merge branch 'v6.3-rc7'

2023-04-21T11:24:18+00:00

Sync with the urgent patches; in particular:

a53ce18cacb4 ("sched/fair: Sanitize vruntime of entity being migrated")

Signed-off-by: Peter Zijlstra

sched/fair: Fix imbalance overflow

2023-04-12T14:46:30+00:00

When local group is fully busy but its average load is above system load,
computing the imbalance will overflow and local group is not the best
target for pulling this load.

Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
Reported-by: Tingjia Cao 
Signed-off-by: Vincent Guittot 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Tingjia Cao 
Link: https://lore.kernel.org/lkml/CABcWv9_DAhVBOq2=W=2ypKE9dKM5s2DvoV8-U0+GDwwuKZ89jQ@mail.gmail.com/T/

sched/numa: use hash_32 to mix up PIDs accessing VMA

2023-04-06T03:03:03+00:00

before: last 6 bits of PID is used as index to store information about
tasks accessing VMA's.

after: hash_32 is used to take of cases where tasks are created over a
period of time, and thus improve collision probability.

Result:
The patch series overall improves autonuma cost.

Kernbench around more than 5% improvement and system time in mmtest
autonuma showed more than 80% improvement

Link: https://lkml.kernel.org/r/d5a9f75513300caed74e5c8570bba9317b963c2b.1677672277.git.raghavendra.kt@amd.com
Signed-off-by: Raghavendra K T 
Suggested-by: Peter Zijlstra 
Cc: Bharata B Rao 
Cc: David Hildenbrand 
Cc: Disha Talreja 
Cc: Ingo Molnar 
Cc: Mel Gorman 
Cc: Mike Rapoport 
Signed-off-by: Andrew Morton

sched/numa: implement access PID reset logic

2023-04-06T03:03:03+00:00

This helps to ensure that only recently accessed PIDs scan the VMAs.

Current implementation: (idea supported by PeterZ)

 1. Accessing PID information is maintained in two windows. 
    access_pids[1] being newest.

 2. Reset old access PID info i.e.  access_pid[0] every (4 *
    sysctl_numa_balancing_scan_delay) interval after initial scan delay
    period expires.

The above interval seemed to be experimentally optimum since it avoids
frequent reset of access info as well as helps clearing the old access
info regularly.  The reset logic is implemented in scan path.

Link: https://lkml.kernel.org/r/f7a675f66d1442d048b4216b2baf94515012c405.1677672277.git.raghavendra.kt@amd.com
Signed-off-by: Raghavendra K T 
Suggested-by: Mel Gorman 
Cc: Bharata B Rao 
Cc: David Hildenbrand 
Cc: Disha Talreja 
Cc: Ingo Molnar 
Cc: Mike Rapoport 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton

sched/numa: enhance vma scanning logic

2023-04-06T03:03:03+00:00

During Numa scanning make sure only relevant vmas of the tasks are
scanned.

Before:
 All the tasks of a process participate in scanning the vma even if they
 do not access vma in it's lifespan.

Now:
 Except cases of first few unconditional scans, if a process do
 not touch vma (exluding false positive cases of PID collisions)
 tasks no longer scan all vma

Logic used:

1) 6 bits of PID used to mark active bit in vma numab status during
   fault to remember PIDs accessing vma.  (Thanks Mel)

2) Subsequently in scan path, vma scanning is skipped if current PID
   had not accessed vma.

3) First two times we do allow unconditional scan to preserve earlier
   behaviour of scanning.

Acknowledgement to Bharata B Rao  for initial patch to
store pid information and Peter Zijlstra  (Usage of
test and set bit)

Link: https://lkml.kernel.org/r/092f03105c7c1d3450f4636b1ea350407f07640e.1677672277.git.raghavendra.kt@amd.com
Signed-off-by: Raghavendra K T 
Suggested-by: Mel Gorman 
Cc: David Hildenbrand 
Cc: Disha Talreja 
Cc: Ingo Molnar 
Cc: Mike Rapoport 
Signed-off-by: Andrew Morton

sched/numa: apply the scan delay to every new vma

2023-04-06T03:03:03+00:00

Pach series "sched/numa: Enhance vma scanning", v3.

The patchset proposes one of the enhancements to numa vma scanning
suggested by Mel.  This is continuation of [3].

Reposting the rebased patchset to akpm mm-unstable tree (March 1) 

Existing mechanism of scan period involves, scan period derived from
per-thread stats.  Process Adaptive autoNUMA [1] proposed to gather NUMA
fault stats at per-process level to capture aplication behaviour better.

During that course of discussion, Mel proposed several ideas to enhance
current numa balancing.  One of the suggestion was below

Track what threads access a VMA.  The suggestion was to use an unsigned
long pid_mask and use the lower bits to tag approximately what threads
access a VMA.  Skip VMAs that did not trap a fault.  This would be
approximate because of PID collisions but would reduce scanning of areas
the thread is not interested in.  The above suggestion intends not to
penalize threads that has no interest in the vma, thus reduce scanning
overhead.

V3 changes are mostly based on PeterZ comments (details below in changes)

Summary of patchset:

Current patchset implements:

1. Delay the vma scanning logic for newly created VMA's so that
   additional overhead of scanning is not incurred for short lived tasks
   (implementation by Mel)

2. Store the information of tasks accessing VMA in 2 windows.  It is
   regularly cleared in (4*sysctl_numa_balancing_scan_delay) interval. 
   The above time is derived from experimenting (Suggested by PeterZ) to
   balance between frequent clearing vs obsolete access data

3. hash_32 used to encode task index accessing VMA information

4. VMA's acess information is used to skip scanning for the tasks
   which had not accessed VMA

Changes since V2:
patch1: 
 - Renaming of structure, macro to function,
 - Add explanation to heuristics
 - Adding more details from result (PeterZ)
 Patch2:
 - Usage of test and set bit (PeterZ)
 - Move storing access PID info to numa_migrate_prep()
 - Add a note on fainess among tasks allowed to scan
   (PeterZ)
 Patch3:
 - Maintain two windows of access PID information
  (PeterZ supported implementation and Gave idea to extend
   to N if needed)
 Patch4:
 - Apply hash_32 function to track VMA accessing PIDs (PeterZ)

Changes since RFC V1:
 - Include Mel's vma scan delay patch
 - Change the accessing pid store logic (Thanks Mel)
 - Fencing structure / code to NUMA_BALANCING (David, Mel)
 - Adding clearing access PID logic (Mel)
 - Descriptive change log ( Mike Rapoport)

Things to ponder over:
==========================================

- Improvement to clearing accessing PIDs logic (discussed in-detail in
  patch3 itself (Done in this patchset by implementing 2 window history)

- Current scan period is not changed in the patchset, so we do see
  frequent tries to scan.  Relaxing scan period dynamically could improve
  results further.

[1] sched/numa: Process Adaptive autoNUMA 
 Link: https://lore.kernel.org/lkml/20220128052851.17162-1-bharata@amd.com/T/

[2] RFC V1 Link: 
  https://lore.kernel.org/all/cover.1673610485.git.raghavendra.kt@amd.com/

[3] V2 Link:
  https://lore.kernel.org/lkml/cover.1675159422.git.raghavendra.kt@amd.com/


Results:
Summary: Huge autonuma cost reduction seen in mmtest. Kernbench improvement 
is more than 5% and huge system time (80%+) improvement from mmtest autonuma.
(dbench had huge std deviation to post)

kernbench
===========
                      6.2.0-mmunstable-base  6.2.0-mmunstable-patched
Amean     user-256    22002.51 (   0.00%)    22649.95 *  -2.94%*
Amean     syst-256    10162.78 (   0.00%)     8214.13 *  19.17%*
Amean     elsp-256      160.74 (   0.00%)      156.92 *   2.38%*

Duration User       66017.43    67959.84
Duration System     30503.15    24657.03
Duration Elapsed      504.61      493.12

                      6.2.0-mmunstable-base  6.2.0-mmunstable-patched
Ops NUMA alloc hit                1738835089.00  1738780310.00
Ops NUMA alloc local              1738834448.00  1738779711.00
Ops NUMA base-page range updates      477310.00      392566.00
Ops NUMA PTE updates                  477310.00      392566.00
Ops NUMA hint faults                   96817.00       87555.00
Ops NUMA hint local faults %           10150.00        2192.00
Ops NUMA hint local percent               10.48           2.50
Ops NUMA pages migrated                86660.00       85363.00
Ops AutoNUMA cost                        489.07         442.14

autonumabench
===============
                      6.2.0-mmunstable-base  6.2.0-mmunstable-patched
Amean     syst-NUMA01                  399.50 (   0.00%)       52.05 *  86.97%*
Amean     syst-NUMA01_THREADLOCAL        0.21 (   0.00%)        0.22 *  -5.41%*
Amean     syst-NUMA02                    0.80 (   0.00%)        0.78 *   2.68%*
Amean     syst-NUMA02_SMT                0.65 (   0.00%)        0.68 *  -3.95%*
Amean     elsp-NUMA01                  313.26 (   0.00%)      313.11 *   0.05%*
Amean     elsp-NUMA01_THREADLOCAL        1.06 (   0.00%)        1.08 *  -1.76%*
Amean     elsp-NUMA02                    3.19 (   0.00%)        3.24 *  -1.52%*
Amean     elsp-NUMA02_SMT                3.72 (   0.00%)        3.61 *   2.92%*

Duration User      396433.47   324835.96
Duration System      2808.70      376.66
Duration Elapsed     2258.61     2258.12

                      6.2.0-mmunstable-base  6.2.0-mmunstable-patched
Ops NUMA alloc hit                  59921806.00    49623489.00
Ops NUMA alloc miss                        0.00           0.00
Ops NUMA interleave hit                    0.00           0.00
Ops NUMA alloc local                59920880.00    49622594.00
Ops NUMA base-page range updates   152259275.00       50075.00
Ops NUMA PTE updates               152259275.00       50075.00
Ops NUMA PMD updates                       0.00           0.00
Ops NUMA hint faults               154660352.00       39014.00
Ops NUMA hint local faults %       138550501.00       23139.00
Ops NUMA hint local percent               89.58          59.31
Ops NUMA pages migrated              8179067.00       14147.00
Ops AutoNUMA cost                     774522.98         195.69


This patch (of 4):

Currently whenever a new task is created we wait for
sysctl_numa_balancing_scan_delay to avoid unnessary scanning overhead. 
Extend the same logic to new or very short-lived VMAs.

[raghavendra.kt@amd.com: add initialization in vm_area_dup())]
Link: https://lkml.kernel.org/r/cover.1677672277.git.raghavendra.kt@amd.com
Link: https://lkml.kernel.org/r/7a6fbba87c8b51e67efd3e74285bb4cb311a16ca.1677672277.git.raghavendra.kt@amd.com
Signed-off-by: Mel Gorman 
Signed-off-by: Raghavendra K T 
Cc: Bharata B Rao 
Cc: David Hildenbrand 
Cc: Ingo Molnar 
Cc: Mike Rapoport 
Cc: Peter Zijlstra 
Cc: Disha Talreja 
Signed-off-by: Andrew Morton

sched/fair: Fix inaccurate tally of ttwu_move_affine

2023-04-05T07:58:48+00:00

There are scenarios where non-affine wakeups are incorrectly counted as
affine wakeups by schedstats.

When wake_affine_idle() returns prev_cpu which doesn't equal to
nr_cpumask_bits, it will slip through the check: target == nr_cpumask_bits
in wake_affine() and be counted as if target == this_cpu in schedstats.

Replace target == nr_cpumask_bits with target != this_cpu to make sure
affine wakeups are accurately tallied.

Fixes: 806486c377e33 (sched/fair: Do not migrate if the prev_cpu is idle)
Suggested-by: Daniel Jordan 
Signed-off-by: Libo Chen 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gautham R. Shenoy 
Link: https://lore.kernel.org/r/20220810223313.386614-1-libo.chen@oracle.com

sched: Interleave cfs bandwidth timers for improved single thread performance at low utilization

2023-03-22T09:10:58+00:00

CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
value set. Hence all period timers would align at expiry.
This happens when there are multiple CPU cgroup's.

There is a performance gain that can be achieved here if the timers are
interleaved when the utilization of each CPU cgroup is low and total
utilization of all the CPU cgroup's is less than 50%. If the timers are
interleaved, then the unthrottled cgroup can run freely without many
context switches and can also benefit from SMT Folding. This effect will
be further amplified in SPLPAR environment.

This commit adds a random offset after initializing each hrtimer. This
would result in interleaving the timers at expiry, which helps in achieving
the said performance gain.

This was tested on powerpc platform with 8 core SMT=8. Socket power was
measured when the workload. Benchmarked the stress-ng with power
information. Throughput oriented benchmarks show significant gain up to
25% while power consumption increases up to 15%.

Workload: stress-ng --cpu=32 --cpu-ops=50000.
1CG - 1 cgroup is running.
2CG - 2 cgroups are running together.
Time taken to complete stress-ng in seconds and power is in watts.
each cgroup is throttled at 25% with 100ms as the period value.
           6.2-rc6                     |   with patch
8 core   1CG    power   2CG     power  |  1CG    power  2 CG    power
        27.5    80.6    40      90     |  27.3    82    32.3    104
        27.5    81      40.2    91     |  27.5    81    38.7     96
        27.7    80      40.1    89     |  27.6    80    29.7    106
        27.7    80.1    40.3    94     |  27.6    80    31.5    105

Latency might be affected by this change. That could happen if the CPU was
in a deep idle state which is possible if we interleave the timers. Used
schbench for measuring the latency. Each cgroup is throttled at 25% with
period value is set to 100ms. Numbers are when both the cgroups are
running simultaneously. Latency values don't degrade much. Some
improvement is seen in tail latencies.

		6.2-rc6        with patch
Groups: 16
50.0th:          39.5            42.5
75.0th:         924.0           922.0
90.0th:         972.0           968.0
95.0th:        1005.5           994.0
99.0th:        4166.0          2287.0
99.5th:        7314.0          7448.0
99.9th:       15024.0         13600.0

Groups: 32
50.0th:         819.0           463.0
75.0th:        1596.0           918.0
90.0th:        5992.0          1281.5
95.0th:       13184.0          2765.0
99.0th:       21792.0         14240.0
99.5th:       25696.0         18920.0
99.9th:       33280.0         35776.0

Groups: 64
50.0th:        4806.0          3440.0
75.0th:       31136.0         33664.0
90.0th:       54144.0         58752.0
95.0th:       66176.0         67200.0
99.0th:       84736.0         91520.0
99.5th:       97408.0        114048.0
99.9th:      136448.0        140032.0

Initial RFC PATCH, discussions and details on the problem:

Link1: https://lore.kernel.org/lkml/5ae3cb09-8c9a-11e8-75a7-cc774d9bc283@linux.vnet.ibm.com/
Link2: https://lore.kernel.org/lkml/9c57c92c-3e0c-b8c5-4be9-8f4df344a347@linux.vnet.ibm.com/
Suggested-by: Peter Zijlstra 
Suggested-by: Thomas Gleixner 
Signed-off-by: Shrikanth Hegde
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Ben Segall 
Reviewed-by: Vincent Guittot 
Link: https://lore.kernel.org/r/20230223185153.1499710-1-sshegde@linux.vnet.ibm.com