Hi all!
I'm seeing an issue with the dw_wdt watchdog on the SoCFPGA ARM
platform with the latest linux-rt v4.18.5-rt4. Actually I seem to
have the same problem, that these patches try to fix:
38a1222ae4f364d5bd5221fe305dbb0889f45d15
Author: Christophe Leroy <christophe.leroy@xxxxxx>
AuthorDate: Fri Dec 8 11:18:35 2017 +0100
Commit: Wim Van Sebroeck <wim@xxxxxxxxx>
CommitDate: Thu Dec 28 20:45:57 2017 +0100
Follows: v4.15-rc3 (345)
Precedes: v4.16-rc1 (13997)
watchdog: core: make sure the watchdog worker always works
When running a command like 'chrt -f 50 dd if=/dev/zero
of=/dev/null',
the watchdog_worker fails to service the HW watchdog and the
HW watchdog fires long before the watchdog soft timeout.
At the moment, the watchdog_worker is invoked as a delayed work.
Delayed works are handled by non realtime kernel threads. The
WQ_HIGHPRI flag only increases the niceness of that threads.
This patch replaces the delayed work logic by kthread delayed
work,
and sets the associated kernel task to SCHED_FIFO with the
highest
priority, in order to ensure that the watchdog worker will run
as
soon as possible.
1ff688209e2ed23f699269b9733993e2ce123fd2
Author: Christophe Leroy <christophe.leroy@xxxxxx>
AuthorDate: Thu Jan 18 12:11:21 2018 +0100
Commit: Wim Van Sebroeck <wim@xxxxxxxxx>
CommitDate: Sun Jan 21 12:44:59 2018 +0100
Follows: v4.15-rc3 (349)
Precedes: v4.16-rc1 (13993)
watchdog: core: make sure the watchdog_worker is not deferred
commit 4cd13c21b207e ("softirq: Let ksoftirqd do its job") has
the
effect of deferring timer handling in case of high CPU load,
hence
delaying the delayed work allthought the worker is running which
high realtime priority.
As hrtimers are not managed by softirqs, this patch replaces the
delayed work by a plain work and uses an hrtimer to schedule
that work.
If I run the same test or 'chrt 50 hackbench 20 -l 150' or any
task where I change the prio with chrt and that runs long enough,
I get a system reset from the watchdog because it times out. This
only happens if the watchdog is already enabled on boot and
CONFIG_PREEMPT_RT_FULL is set.
Any idea if I'm missing something essential? If I understand it
correctly, the two commits fix the framework and therefore the
dw_wdt driver doesn't need any updates.
Best regards,
Steffen
--
Pengutronix e.K. | Steffen Trumtrar
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