A few months ago I implemented debug messages in the command stream by
stuffing the unused bits of MI_NOOP :
https://patchwork.freedesktop.org/series/26079/
Aubinator would then read the bits and print the messages.
We might be able to reuse similar idea to get away with any external
interface.
Instead of having strings of characters we could put a marker with the
BO handle that could be used to store all of the metadata about a
particular draw call.
What do you think?
-
Lionel
On 27/09/17 07:53, Rogovin, Kevin wrote:
Hi,
Right now the way the thing works is that it walks the batchbuffer just after the
kernel returns from the ioctl and updates its internal view of the GPU state as it walks
and emits to the log file the data. The log on a single batchbuffer is (essentially) just
a list of call ID's from the apitrace together of "where in the batchbuffer"
that call started.
I confess that I had not realized the potential application for using
something like this to help diagnose GPU hangs! I think it is a really good
idea. What I could do is the following (and it is not terribly hard to do):
1. -BEFORE- issuing the ioctl, the logger walks just the api markers in the
log of the batchbuffer, and makes a new GEM BO filled with apitrace data (call
ID, and maybe GL function data) and modify the ioctl to have an extra buffer.
2. -AFTER- the ioctl returns, emit the log data (as now) and delete the GEM
BO; In order to read the GPU state more accurately I need to walk the log and
update the GPU state after the ioctl (mostly out of paranoia for values copied
from BO's to pipeline registers).
What would happen, is that if a batchbuffer made the GPU hang, you would then
know all the GL commands (trace ID's from the API trace) that made stuff on
that batchbuffer. Then one could go back to the apitrace of the troublesome
application and have a much better starting place to debug.
We could also do something evil looking and put another modification on
apitrace where it can have a list of call trace ranges where it inserts
glFinish after each call. Those glFinish()'s will then force the ioctl of the
exact troublesome draw call without needing to tell i965 to flush after each
draw call.
Just to make sure, you want the "apitrace" data (call ID list, maybe function
name) in a GEM BO? Which GEM BO should it be in the list so that kernel debug code know
which one to use to dump? I would guess if the batchbuffer is the first buffer, then it
would be the last buffer, otherwise if the batch buffer is the last one, I guess it would
be one just before, but that might screw up reloc-data if any of the relocs in the
batchbuffer refer to itself. I can also emit the data to a file and close the file before
the ioctl and if the ioctl returns, delete said file (assuming a GPU hang always stops
the process, then a hang would leave behind a file).
Let me know, what is best, and I will do it.
-Kevin
-----Original Message-----
From: Chris Wilson [mailto:ch...@chris-wilson.co.uk]
Sent: Tuesday, September 26, 2017 11:20 PM
To: Rogovin, Kevin <kevin.rogo...@intel.com>; mesa-dev@lists.freedesktop.org
Subject: Re: [Mesa-dev] [PATCH 00/22] RFC: Batchbuffer Logger for Intel GPU
Quoting Rogovin, Kevin (2017-09-26 10:35:44)
Hi,
Attached to this message are the following:
1. a file giving example usage of the tool with a modified
apitrace to produce json output
2. the patches to apitrace to make it BatchbufferLogger aware
3. the JSON files (gzipped) made from the example.
I encourage (and hope) people will take a look at the JSON to see the potential
of the tool.
The automatic apitrace-esque logging seems very useful. How easy would it be to
write that trace into a bo and associate with the execbuffer (from my pov, it
should be that hard)? That way you could get the most recent actions before a
GPU hang, attach them to a bug and decode them at leisure. (An extension may be
to keep a ring of the last N traces so that you can see some setup a few
batches ago that triggered a hang in this one.)
I presume you already have such a plan, and I'm just preaching to the choir.
-Chris
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