mirror of
https://github.com/torvalds/linux.git
synced 2024-09-20 06:53:04 +00:00
409faf8c97
When running the vmalloc stress on a 448-core system, observe the average
latency of purge_vmap_node() is about 2 seconds by using the eBPF/bcc
'funclatency.py' tool [1].
# /your-git-repo/bcc/tools/funclatency.py -u purge_vmap_node & pid1=$! && sleep 8 && modprobe test_vmalloc nr_threads=$(nproc) run_test_mask=0x7; kill -SIGINT $pid1
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 29 | |
4 -> 7 : 19 | |
8 -> 15 : 56 | |
16 -> 31 : 483 |**** |
32 -> 63 : 1548 |************ |
64 -> 127 : 2634 |********************* |
128 -> 255 : 2535 |********************* |
256 -> 511 : 1776 |************** |
512 -> 1023 : 1015 |******** |
1024 -> 2047 : 573 |**** |
2048 -> 4095 : 488 |**** |
4096 -> 8191 : 1091 |********* |
8192 -> 16383 : 3078 |************************* |
16384 -> 32767 : 4821 |****************************************|
32768 -> 65535 : 3318 |*************************** |
65536 -> 131071 : 1718 |************** |
131072 -> 262143 : 2220 |****************** |
262144 -> 524287 : 1147 |********* |
524288 -> 1048575 : 1179 |********* |
1048576 -> 2097151 : 822 |****** |
2097152 -> 4194303 : 906 |******* |
4194304 -> 8388607 : 2148 |***************** |
8388608 -> 16777215 : 4497 |************************************* |
16777216 -> 33554431 : 289 |** |
avg = 2041714 usecs, total: 78381401772 usecs, count: 38390
The worst case is over 16-33 seconds, so soft lockup is triggered [2].
[Root Cause]
1) Each purge_list has the long list. The following shows the number of
vmap_area is purged.
crash> p vmap_nodes
vmap_nodes = $27 = (struct vmap_node *) 0xff2de5a900100000
crash> vmap_node 0xff2de5a900100000 128 | grep nr_purged
nr_purged = 663070
...
nr_purged = 821670
nr_purged = 692214
nr_purged = 726808
...
2) atomic_long_sub() employs the 'lock' prefix to ensure the atomic
operation when purging each vmap_area. However, the iteration is over
600000 vmap_area (See 'nr_purged' above).
Here is objdump output:
$ objdump -D vmlinux
ffffffff813e8c80 <purge_vmap_node>:
...
ffffffff813e8d70: f0 48 29 2d 68 0c bb lock sub %rbp,0x2bb0c68(%rip)
...
Quote from "Instruction tables" pdf file [3]:
Instructions with a LOCK prefix have a long latency that depends on
cache organization and possibly RAM speed. If there are multiple
processors or cores or direct memory access (DMA) devices, then all
locked instructions will lock a cache line for exclusive access,
which may involve RAM access. A LOCK prefix typically costs more
than a hundred clock cycles, even on single-processor systems.
That's why the latency of purge_vmap_node() dramatically increases
on a many-core system: One core is busy on purging each vmap_area of
the *long* purge_list and executing atomic_long_sub() for each
vmap_area, while other cores free vmalloc allocations and execute
atomic_long_add_return() in free_vmap_area_noflush().
[Solution]
Employ a local variable to record the total purged pages, and execute
atomic_long_sub() after the traversal of the purge_list is done. The
experiment result shows the latency improvement is 99%.
[Experiment Result]
1) System Configuration: Three servers (with HT-enabled) are tested.
* 72-core server: 3rd Gen Intel Xeon Scalable Processor*1
* 192-core server: 5th Gen Intel Xeon Scalable Processor*2
* 448-core server: AMD Zen 4 Processor*2
2) Kernel Config
* CONFIG_KASAN is disabled
3) The data in column "w/o patch" and "w/ patch"
* Unit: micro seconds (us)
* Each data is the average of 3-time measurements
System w/o patch (us) w/ patch (us) Improvement (%)
--------------- -------------- ------------- -------------
72-core server 2194 14 99.36%
192-core server 143799 1139 99.21%
448-core server 1992122 6883 99.65%
[1] https://github.com/iovisor/bcc/blob/master/tools/funclatency.py
[2] https://gist.github.com/AdrianHuang/37c15f67b45407b83c2d32f918656c12
[3] https://www.agner.org/optimize/instruction_tables.pdf
Link: https://lkml.kernel.org/r/20240829130633.2184-1-ahuang12@lenovo.com
Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
||
|---|---|---|
| .. | ||
| damon | ||
| kasan | ||
| kfence | ||
| kmsan | ||
| backing-dev.c | ||
| balloon_compaction.c | ||
| bootmem_info.c | ||
| cma_debug.c | ||
| cma_sysfs.c | ||
| cma.c | ||
| cma.h | ||
| compaction.c | ||
| debug_page_alloc.c | ||
| debug_page_ref.c | ||
| debug_vm_pgtable.c | ||
| debug.c | ||
| dmapool_test.c | ||
| dmapool.c | ||
| early_ioremap.c | ||
| execmem.c | ||
| fadvise.c | ||
| fail_page_alloc.c | ||
| failslab.c | ||
| filemap.c | ||
| folio-compat.c | ||
| gup_test.c | ||
| gup_test.h | ||
| gup.c | ||
| highmem.c | ||
| hmm.c | ||
| huge_memory.c | ||
| hugetlb_cgroup.c | ||
| hugetlb_vmemmap.c | ||
| hugetlb_vmemmap.h | ||
| hugetlb.c | ||
| hwpoison-inject.c | ||
| init-mm.c | ||
| internal.h | ||
| interval_tree.c | ||
| io-mapping.c | ||
| ioremap.c | ||
| Kconfig | ||
| Kconfig.debug | ||
| khugepaged.c | ||
| kmemleak.c | ||
| ksm.c | ||
| list_lru.c | ||
| maccess.c | ||
| madvise.c | ||
| Makefile | ||
| mapping_dirty_helpers.c | ||
| memblock.c | ||
| memcontrol-v1.c | ||
| memcontrol-v1.h | ||
| memcontrol.c | ||
| memfd.c | ||
| memory_hotplug.c | ||
| memory-failure.c | ||
| memory-tiers.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| memremap.c | ||
| memtest.c | ||
| migrate_device.c | ||
| migrate.c | ||
| mincore.c | ||
| mlock.c | ||
| mm_init.c | ||
| mm_slot.h | ||
| mmap_lock.c | ||
| mmap.c | ||
| mmu_gather.c | ||
| mmu_notifier.c | ||
| mmzone.c | ||
| mprotect.c | ||
| mremap.c | ||
| mseal.c | ||
| msync.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_counter.c | ||
| page_ext.c | ||
| page_idle.c | ||
| page_io.c | ||
| page_isolation.c | ||
| page_owner.c | ||
| page_poison.c | ||
| page_reporting.c | ||
| page_reporting.h | ||
| page_table_check.c | ||
| page_vma_mapped.c | ||
| page-writeback.c | ||
| pagewalk.c | ||
| percpu-internal.h | ||
| percpu-km.c | ||
| percpu-stats.c | ||
| percpu-vm.c | ||
| percpu.c | ||
| pgalloc-track.h | ||
| pgtable-generic.c | ||
| process_vm_access.c | ||
| ptdump.c | ||
| readahead.c | ||
| rmap.c | ||
| rodata_test.c | ||
| secretmem.c | ||
| shmem_quota.c | ||
| shmem.c | ||
| show_mem.c | ||
| shrinker_debug.c | ||
| shrinker.c | ||
| shuffle.c | ||
| shuffle.h | ||
| slab_common.c | ||
| slab.h | ||
| slub.c | ||
| sparse-vmemmap.c | ||
| sparse.c | ||
| swap_cgroup.c | ||
| swap_slots.c | ||
| swap_state.c | ||
| swap.c | ||
| swap.h | ||
| swapfile.c | ||
| truncate.c | ||
| usercopy.c | ||
| userfaultfd.c | ||
| util.c | ||
| vmalloc.c | ||
| vmpressure.c | ||
| vmscan.c | ||
| vmstat.c | ||
| workingset.c | ||
| z3fold.c | ||
| zbud.c | ||
| zpool.c | ||
| zsmalloc.c | ||
| zswap.c | ||