On Wed, 6 Mar 2024, Andrew Stubbs wrote: > On 06/03/2024 12:09, Thomas Schwinge wrote: > > Hi! > > > > On 2024-02-21T17:32:13+0100, Richard Biener <rguent...@suse.de> wrote: > >> Am 21.02.2024 um 13:34 schrieb Thomas Schwinge <tschwi...@baylibre.com>: > >>> [...] per my work on <https://gcc.gnu.org/PR66005> > >>> "libgomp make check time is excessive", all execution testing in libgomp > >>> is serialized in 'libgomp/testsuite/lib/libgomp.exp:libgomp_load'. [...] > >>> (... with the caveat that execution tests for > >>> effective-targets are *not* governed by that, as I've found yesterday. > >>> I have a WIP hack for that, too.) > > > >>> What disturbs the testing a lot is, that the GPU may get into a bad > >>> state, upon which any use either fails with a > >>> 'HSA_STATUS_ERROR_OUT_OF_RESOURCES' error -- or by just hanging, deep in > >>> 'libhsa-runtime64.so.1'... > >>> > >>> I've now tried to debug the latter case (hang). When the GPU gets into > >>> this bad state (whatever exactly that is), > >>> 'hsa_executable_load_code_object' still returns 'HSA_STATUS_SUCCESS', but > >>> then GCN target execution ('gcn-run') hangs in 'hsa_executable_freeze' > >>> vs. GCN offloading execution ('libgomp-plugin-gcn.so.1') hangs right > >>> before 'hsa_executable_freeze', in the GCN heap setup 'hsa_memory_copy'. > >>> There it hangs until killed (for example, until DejaGnu's timeout > >>> mechanism kills the process -- just that the next GPU-using execution > >>> test then runs into the same thing again...). > >>> > >>> In this state (and also the 'HSA_STATUS_ERROR_OUT_OF_RESOURCES' state), > >>> we're able to recover via: > >>> > >>> $ flock /tmp/gpu.lock sudo cat > >>> /sys/kernel/debug/dri/0/amdgpu_gpu_recover > >>> 0 > > > > At least most of the times. I've found that -- sometimes... ;-( -- if > > you run into 'HSA_STATUS_ERROR_OUT_OF_RESOURCES', then do > > 'amdgpu_gpu_recover', and then immediately re-execute, you'll again run > > into 'HSA_STATUS_ERROR_OUT_OF_RESOURCES'. That appears to be avoidable > > by injecting some artificial "cool-down period"... (The latter I've not > > yet tested extensively.) > > > >>> This is, obviously, a hack, probably needs a serial lock to not disturb > >>> other things, has hard-coded 'dri/0', and as I said in > >>> <https://inbox.sourceware.org/87plww8qin....@euler.schwinge.ddns.net> > >>> "GCN RDNA2+ vs. GCC SLP vectorizer": > >>> > >>> | I've no idea what > >>> | 'amdgpu_gpu_recover' would do if the GPU is also used for display. > >> > >> It ends up terminating your X session? > > > > Eh.... ;'-| > > > >> (there?s some automatic driver recovery that?s also sometimes triggered > >> which sounds like the same thing). > > > >> I need to try using the integrated graphics for X11 to see if that avoids > >> the issue. > > > > A few years ago, I tried that for a Nvidia GPU laptop, and -- if I now > > remember correctly -- basically got it to work, via hand-editing > > '/etc/X11/xorg.conf' and all that... But: I couldn't get external HDMI > > to work in that setup, and therefore reverted to "standard". > > > >> Guess AMD needs to improve the driver/runtime (or we - it?s open source at > >> least up to the firmware). > > > >>> However, it's very useful in my testing. :-| > >>> > >>> The questions is, how to detect the "hang" state without first running > >>> into a timeout (and disambiguating such a timeout from a user code > >>> timeout)? Add a watchdog: call 'alarm([a few seconds])' before device > >>> initialization, and before the actual GPU kernel launch cancel it with > >>> 'alarm(0)'? (..., and add a handler for 'SIGALRM' to print a distinct > >>> error message that we can then react on, like for > >>> 'HSA_STATUS_ERROR_OUT_OF_RESOURCES'.) Probably 'alarm'/'SIGALRM' is a > >>> no-go in libgomp -- instead, use a helper thread to similarly implement a > >>> watchdog? ('libgomp/plugin/plugin-gcn.c' already is using pthreads for > >>> other purposes.) Any other clever ideas? What's a suitable value for > >>> "a few seconds"? > > > > I'm attaching my current "GCN: Watchdog for device image load", covering > > both 'gcc/config/gcn/gcn-run.cc' and 'libgomp/plugin/plugin-gcn.c'. > > (That's using 'timer_create' etc. instead of 'alarm'/'SIGALRM'. ) > > > > That, plus routing *all* potential GPU usage (in particular: including > > execution tests for effective-targets, see above) through a serial lock > > ('flock', implemented in DejaGnu board file, outside of the the > > "DejaGnu timeout domain", similar to > > 'libgomp/testsuite/lib/libgomp.exp:libgomp_load', see above), plus > > catching 'HSA_STATUS_ERROR_OUT_OF_RESOURCES' (both the "real" ones and > > the "fake" ones via "GCN: Watchdog for device image load") and in that > > case 'amdgpu_gpu_recover' and re-execution of the respective executable, > > does greatly stabilize flaky GCN target/offloading testing. > > > > Do we have consensus to move forward with this approach, generally? > > I've also observed a number of random hangs in host-side code outside our > control, but after the kernel has exited. In general this watchdog approach > might help with these. I do feel like it's "papering over the cracks", but if > we can't fix it.... at the end of the day it's just a little extra code.
I wonder if you maybe have contact to people at AMD that are willing to debug this and improve the driver side of this? I'm seeing quite a number of similar reports for the issue I hit in the github tracker, multiple years old and also current, so that doesn't seem to be a good way to get things fixed ... Richard. > My only concern is that it might actually cause failures, perhaps on heavily > loaded systems, or with network filesystems, or during debugging. > > Andrew >
