On 03/11/2022 09:18, Tvrtko Ursulin wrote:
On 03/11/2022 01:33, John Harrison wrote:
On 11/2/2022 07:20, Tvrtko Ursulin wrote:
On 02/11/2022 12:12, Jani Nikula wrote:
On Tue, 01 Nov 2022, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
At the end of each test, IGT does a drop caches call via sysfs with
sysfs?
Sorry, that was meant to say debugfs. I've also been working on some
sysfs IGT issues and evidently got my wires crossed!
special flags set. One of the possible paths waits for idle with an
infinite timeout. That causes problems for debugging issues when CI
catches a "can't go idle" test failure. Best case, the CI system times
out (after 90s), attempts a bunch of state dump actions and then
reboots the system to recover it. Worst case, the CI system can't do
anything at all and then times out (after 1000s) and simply reboots.
Sometimes a serial port log of dmesg might be available, sometimes
not.
So rather than making life hard for ourselves, change the timeout to
be 10s rather than infinite. Also, trigger the standard
wedge/reset/recover sequence so that testing can continue with a
working system (if possible).
Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_debugfs.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
b/drivers/gpu/drm/i915/i915_debugfs.c
index ae987e92251dd..9d916fbbfc27c 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -641,6 +641,9 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_perf_noa_delay_fops,
DROP_RESET_ACTIVE | \
DROP_RESET_SEQNO | \
DROP_RCU)
+
+#define DROP_IDLE_TIMEOUT (HZ * 10)
I915_IDLE_ENGINES_TIMEOUT is defined in i915_drv.h. It's also only used
here.
So move here, dropping i915 prefix, next to the newly proposed one?
Sure, can do that.
I915_GEM_IDLE_TIMEOUT is defined in i915_gem.h. It's only used in
gt/intel_gt.c.
Move there and rename to GT_IDLE_TIMEOUT?
I915_GT_SUSPEND_IDLE_TIMEOUT is defined and used only in intel_gt_pm.c.
No action needed, maybe drop i915 prefix if wanted.
These two are totally unrelated and in code not being touched by this
change. I would rather not conflate changing random other things with
fixing this specific issue.
I915_IDLE_ENGINES_TIMEOUT is in ms, the rest are in jiffies.
Add _MS suffix if wanted.
My head spins.
I follow and raise that the newly proposed DROP_IDLE_TIMEOUT applies
to DROP_ACTIVE and not only DROP_IDLE.
My original intention for the name was that is the 'drop caches
timeout for intel_gt_wait_for_idle'. Which is quite the mouthful and
hence abbreviated to DROP_IDLE_TIMEOUT. But yes, I realised later that
name can be conflated with the DROP_IDLE flag. Will rename.
Things get refactored, code moves around, bits get left behind, who
knows. No reason to get too worked up. :) As long as people are
taking a wider view when touching the code base, and are not afraid
to send cleanups, things should be good.
On the other hand, if every patch gets blocked in code review because
someone points out some completely unrelated piece of code could be a
bit better then nothing ever gets fixed. If you spot something that
you think should be improved, isn't the general idea that you should
post a patch yourself to improve it?
There's two maintainers per branch and an order of magnitude or two more
developers so it'd be nice if cleanups would just be incoming on
self-initiative basis. ;)
For the actual functional change at hand - it would be nice if code
paths in question could handle SIGINT and then we could punt the
decision on how long someone wants to wait purely to userspace. But
it's probably hard and it's only debugfs so whatever.
The code paths in question will already abort on a signal won't they?
Both intel_gt_wait_for_idle() and intel_guc_wait_for_pending_msg(),
which is where the uc_wait_for_idle eventually ends up, have an
'if(signal_pending) return -EINTR;' check. Beyond that, it sounds like
what you are asking for is a change in the IGT libraries and/or CI
framework to start sending signals after some specific timeout. That
seems like a significantly more complex change (in terms of the number
of entities affected and number of groups involved) and unnecessary.
If you say so, I haven't looked at them all. But if the code path in
question already aborts on signals then I am not sure what is the patch
fixing? I assumed you are trying to avoid the write stuck in D forever,
which then prevents driver unload and everything, requiring the test
runner to eventually reboot. If you say SIGINT works then you can
already recover from userspace, no?
Whether or not 10s is enough CI will hopefully tell us. I'd probably
err on the side of safety and make it longer, but at most half from
the test runner timeout.
This is supposed to be test clean up. This is not about how long a
particular test takes to complete but about how long it takes to
declare the system broken after the test has already finished. I would
argue that even 10s is massively longer than required.
I am not convinced that wedging is correct though. Conceptually could
be just that the timeout is too short. What does wedging really give
us, on top of limiting the wait, when latter AFAIU is the key factor
which would prevent the need to reboot the machine?
It gives us a system that knows what state it is in. If we can't idle
the GT then something is very badly wrong. Wedging indicates that. It
also ensure that a full GT reset will be attempted before the next
test is run. Helping to prevent a failure on test X from propagating
into failures of unrelated tests X+1, X+2, ... And if the GT reset
does not work because the system is really that badly broken then
future tests will not run rather than report erroneous failures.
This is not about getting a more stable system for end users by
sweeping issues under the carpet and pretending all is well. End users
don't run IGTs or explicitly call dodgy debugfs entry points. The sole
motivation here is to get more accurate results from CI. That is,
correctly identifying which test has hit a problem, getting valid
debug analysis for that test (logs and such) and allowing further
testing to complete correctly in the case where the system can be
recovered.
I don't really oppose shortening of the timeout in principle, just want
a clear statement if this is something IGT / test runner could already
do or not. It can apply a timeout, it can also send SIGINT, and it could
even trigger a reset from outside. Sure it is debugfs hacks so general
"kernel should not implement policy" need not be strictly followed, but
lets have it clear what are the options.
One conceptual problem with applying this policy is that the code is:
if (val & (DROP_IDLE | DROP_ACTIVE)) {
ret = intel_gt_wait_for_idle(gt, MAX_SCHEDULE_TIMEOUT);
if (ret)
return ret;
}
if (val & DROP_IDLE) {
ret = intel_gt_pm_wait_for_idle(gt);
if (ret)
return ret;
}
So if someone passes in DROP_IDLE and then why would only the first
branch have a short timeout and wedge. Yeah some bug happens to be there
at the moment, but put a bug in a different place and you hang on the
second branch and then need another patch. Versus perhaps making it all
respect SIGINT and handle from outside.
Regards,
Tvrtko
