On Tue, Jun 16, 2020 at 06:32:48PM +0200, Sebastian Andrzej Siewior wrote: > On 2020-06-16 13:11:51 [-0300], Marcelo Tosatti wrote: > > Remote draining of pages was removed from 5.6-rt. > > > > Unfortunately its necessary for use-cases which have a busy spinning > > SCHED_FIFO thread on isolated CPU: > > > > [ 7475.821066] INFO: task ld:274531 blocked for more than 600 seconds. > > [ 7475.822157] Not tainted 4.18.0-208.rt5.20.el8.x86_64 #1 > > [ 7475.823094] echo 0 /proc/sys/kernel/hung_task_timeout_secs disables this message. > > [ 7475.824392] ld D 0 274531 274530 0x00084080 > > [ 7475.825307] Call Trace: > > [ 7475.825761] __schedule+0x342/0x850 > > [ 7475.826377] schedule+0x39/0xd0 > > [ 7475.826923] schedule_timeout+0x20e/0x410 > > [ 7475.827610] ? __schedule+0x34a/0x850 > > [ 7475.828247] ? ___preempt_schedule+0x16/0x18 > > [ 7475.828953] wait_for_completion+0x85/0xe0 > > [ 7475.829653] flush_work+0x11a/0x1c0 > > [ 7475.830313] ? flush_workqueue_prep_pwqs+0x130/0x130 > > [ 7475.831148] drain_all_pages+0x140/0x190 > > [ 7475.831803] __alloc_pages_slowpath+0x3f8/0xe20 > > [ 7475.832571] ? mem_cgroup_commit_charge+0xcb/0x510 > > [ 7475.833371] __alloc_pages_nodemask+0x1ca/0x2b0 > > [ 7475.834134] pagecache_get_page+0xb5/0x2d0 > > [ 7475.834814] ? account_page_dirtied+0x11a/0x220 > > [ 7475.835579] grab_cache_page_write_begin+0x1f/0x40 > > [ 7475.836379] iomap_write_begin.constprop.44+0x1c1/0x370 > > [ 7475.837241] ? iomap_write_end+0x91/0x290 > > [ 7475.837911] iomap_write_actor+0x92/0x170 > > ... > > > > So enable remote draining again. > > Is upstream affected by this? And if not, why not? It is affected. The workqueue thread for a given CPU is SCHED_OTHER, which can't interrupt a SCHED_FIFO task which does not sleep.
