On Sat, Jun 22, 2024 at 12:58:08AM -0300, Leonardo Bras wrote: > The problem: > Some places in the kernel implement a parallel programming strategy > consisting on local_locks() for most of the work, and some rare remote > operations are scheduled on target cpu. This keeps cache bouncing low since > cacheline tends to be mostly local, and avoids the cost of locks in non-RT > kernels, even though the very few remote operations will be expensive due > to scheduling overhead. > > On the other hand, for RT workloads this can represent a problem: getting > an important workload scheduled out to deal with remote requests is > sure to introduce unexpected deadline misses. Another hang with a busy polling workload (kernel update hangs on grub2-probe): [342431.665417] INFO: task grub2-probe:24484 blocked for more than 622 seconds. [342431.665458] Tainted: G W X ------- --- 5.14.0-438.el9s.x86_64+rt #1 [342431.665488] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [342431.665515] task:grub2-probe state:D stack:0 pid:24484 ppid:24455 flags:0x00004002 [342431.665523] Call Trace: [342431.665525] <TASK> [342431.665527] __schedule+0x22a/0x580 [342431.665537] schedule+0x30/0x80 [342431.665539] schedule_timeout+0x153/0x190 [342431.665543] ? preempt_schedule_thunk+0x16/0x30 [342431.665548] ? preempt_count_add+0x70/0xa0 [342431.665554] __wait_for_common+0x8b/0x1c0 [342431.665557] ? __pfx_schedule_timeout+0x10/0x10 [342431.665560] __flush_work.isra.0+0x15b/0x220 [342431.665565] ? __pfx_wq_barrier_func+0x10/0x10 [342431.665570] __lru_add_drain_all+0x17d/0x220 [342431.665576] invalidate_bdev+0x28/0x40 [342431.665583] blkdev_common_ioctl+0x714/0xa30 [342431.665588] ? bucket_table_alloc.isra.0+0x1/0x150 [342431.665593] ? cp_new_stat+0xbb/0x180 [342431.665599] blkdev_ioctl+0x112/0x270 [342431.665603] ? security_file_ioctl+0x2f/0x50 [342431.665609] __x64_sys_ioctl+0x87/0xc0 [342431.665614] do_syscall_64+0x5c/0xf0 [342431.665619] ? __ct_user_enter+0x89/0x130 [342431.665623] ? syscall_exit_to_user_mode+0x22/0x40 [342431.665625] ? do_syscall_64+0x6b/0xf0 [342431.665627] ? __ct_user_enter+0x89/0x130 [342431.665629] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [342431.665635] RIP: 0033:0x7f39856c757b [342431.665666] RSP: 002b:00007ffd9541c488 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [342431.665670] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f39856c757b [342431.665673] RDX: 0000000000000000 RSI: 0000000000001261 RDI: 0000000000000005 [342431.665674] RBP: 00007ffd9541c540 R08: 0000000000000003 R09: 006164732f766564 [342431.665676] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd9543ca68 [342431.665678] R13: 000055ea758a0708 R14: 000055ea759de338 R15: 00007f398586f000
