Messages in this thread | | | Subject | Re: [PATCH 0/9] sched: Migrate disable support | From | Dietmar Eggemann <> | Date | Fri, 25 Sep 2020 11:12:09 +0200 |
| |
On 21/09/2020 18:35, Peter Zijlstra wrote: > Hi, > > Here's my take on migrate_disable(). It avoids growing a second means of > changing the affinity, documents how the things violates locking rules but > still mostly works. > > It also avoids blocking completely, so no more futex band-aids required. > > Also, no more atomics/locks on the fast path. > > I also put in a comment that explains how the whole concept is fundamentally > flawed but a necessary evil to get PREEMPT_RT going -- for now. > > Somewhat tested with PREEMPT_RT. > > --- > include/linux/cpuhotplug.h | 1 > include/linux/preempt.h | 60 +++ > include/linux/sched.h | 4 > include/linux/sched/hotplug.h | 2 > include/linux/stop_machine.h | 5 > kernel/cpu.c | 9 > kernel/sched/core.c | 673 +++++++++++++++++++++++++++++++----------- > kernel/sched/deadline.c | 5 > kernel/sched/sched.h | 24 + > kernel/stop_machine.c | 23 + > lib/dump_stack.c | 2 > lib/smp_processor_id.c | 5 > 12 files changed, 635 insertions(+), 178 deletions(-) >
I get this when running 6 (periodic) RT50 tasks with CPU hp stress on my 6 CPU JUNO board (!CONFIG_PREEMPT_RT).
[ 55.490263] ------------[ cut here ]------------ [ 55.505261] Modules linked in: [ 55.508322] CPU: 3 PID: 24 Comm: migration/3 Not tainted 5.9.0-rc1-00132-gc096e6406c50-dirty #90 [ 55.517119] Hardware name: ARM Juno development board (r0) (DT) [ 55.523058] Stopper: multi_cpu_stop+0x0/0x170 <- 0x0 [ 55.528029] pstate: 20000085 (nzCv daIf -PAN -UAO BTYPE=--) [ 55.533612] pc : sched_cpu_dying+0x124/0x130 [ 55.537887] lr : sched_cpu_dying+0xd8/0x130 [ 55.542071] sp : ffff800011f0bca0 [ 55.545385] x29: ffff800011f0bca0 x28: 0000000000000002 [ 55.550703] x27: 0000000000000000 x26: 0000000000000060 [ 55.556022] x25: 0000000000000000 x24: 0000000000000001 [ 55.561340] x23: 0000000000000000 x22: 0000000000000003 [ 55.566659] x21: 0000000000000080 x20: 0000000000000003 [ 55.571977] x19: ffff00097ef9e1c0 x18: 0000000000000010 [ 55.577295] x17: 0000000000000000 x16: 0000000000000000 [ 55.582613] x15: 0000000000000000 x14: 000000000000015c [ 55.587932] x13: 0000000000000000 x12: 00000000000006f1 [ 55.593250] x11: 0000000000000080 x10: 0000000000000000 [ 55.598567] x9 : 0000000000000003 x8 : ffff0009743f5900 [ 55.603886] x7 : 0000000000000003 x6 : 0000000000000000 [ 55.609204] x5 : 0000000000000001 x4 : 0000000000000002 [ 55.614521] x3 : 0000000000000000 x2 : 0000000000000013 [ 55.619839] x1 : 0000000000000008 x0 : 0000000000000003 [ 55.625158] Call trace: [ 55.627607] sched_cpu_dying+0x124/0x130 [ 55.631535] cpuhp_invoke_callback+0x88/0x210 [ 55.635897] take_cpu_down+0x7c/0xd8 [ 55.639475] multi_cpu_stop+0xac/0x170 [ 55.643227] cpu_stopper_thread+0x98/0x130 [ 55.647327] smpboot_thread_fn+0x1c4/0x280 [ 55.651427] kthread+0x140/0x160 [ 55.654658] ret_from_fork+0x10/0x34 [ 55.658239] Code: f000e1c1 913fc021 1400034a 17ffffde (d4210000) [ 55.664342] ---[ end trace c5b8988b7b701e56 ]--- [ 55.668963] note: migration/3[24] exited with preempt_count 3
7309 int sched_cpu_dying(unsigned int cpu) ... BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq)); ...
rq->nr_running is always 2 here in this cases.
balance_hotplug_wait and sched_cpu_wait_empty run in cpuhp/X (CFS) whereas sched_cpu_dying in migration/X ?
| |