Re: [RFC 3/3] drm/msm: Add comm/cmdline fields
From: Tvrtko Ursulin
Date: Wed Apr 19 2023 - 09:36:47 EST
On 18/04/2023 15:56, Rob Clark wrote:
On Tue, Apr 18, 2023 at 1:53 AM Tvrtko Ursulin
<tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
On 17/04/2023 21:12, Rob Clark wrote:
From: Rob Clark <robdclark@xxxxxxxxxxxx>
Normally this would be the same information that can be obtained in
other ways. But in some cases the process opening the drm fd is merely
a sort of proxy for the actual process using the GPU. This is the case
for guest VM processes using the GPU via virglrenderer, in which case
the msm native-context renderer in virglrenderer overrides the comm/
cmdline to be the guest process's values.
Exposing this via fdinfo allows tools like gputop to show something more
meaningful than just a bunch of "pcivirtio-gpu" users.
You also later expanded with:
"""
I should have also mentioned, in the VM/proxy scenario we have a
single process with separate drm_file's for each guest VM process. So
it isn't an option to just change the proxy process's name to match
the client.
"""
So how does that work - this single process temporarily changes it's
name for each drm fd it opens and creates a context or it is actually in
the native context protocol?
It is part of the protocol, the mesa driver in the VM sends[1] this
info to the native-context "shim" in host userspace which uses the
SET_PARAM ioctl to pass this to the kernel. In the host userspace
there is just a single process (you see the host PID below) but it
does a separate open() of the drm dev for each guest process (so that
they each have their own GPU address space for isolation):
DRM minor 128
PID MEM ACTIV NAME gpu
5297 200M 82M com.mojang.minecr |██████████████▏ |
1859 199M 0B chrome |█▉ |
5297 64M 9M surfaceflinger | |
5297 12M 0B org.chromium.arc. | |
5297 12M 0B com.android.syste | |
5297 12M 0B org.chromium.arc. | |
5297 26M 0B com.google.androi | |
5297 65M 0B system_server | |
[1] https://gitlab.freedesktop.org/virgl/virglrenderer/-/blob/master/src/drm/msm/msm_proto.h#L326
[2] https://gitlab.freedesktop.org/virgl/virglrenderer/-/blob/master/src/drm/msm/msm_renderer.c#L1050
Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
---
Documentation/gpu/drm-usage-stats.rst | 8 ++++++++
drivers/gpu/drm/msm/msm_gpu.c | 14 ++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst
index 8e00d53231e0..bc90bed455e3 100644
--- a/Documentation/gpu/drm-usage-stats.rst
+++ b/Documentation/gpu/drm-usage-stats.rst
@@ -148,6 +148,14 @@ percentage utilization of the engine, whereas drm-engine-<keystr> only reflects
time active without considering what frequency the engine is operating as a
percentage of it's maximum frequency.
+- drm-comm: <valstr>
+
+Returns the clients executable path.
Full path and not just current->comm? In this case probably give it a
more descriptive name here.
drm-client-executable
drm-client-command-line
So we stay in the drm-client- namespace?
Or if the former is absolute path could one key be enough for both?
drm-client-command-line: /path/to/executable --arguments
comm and cmdline can be different. Android seems to change the comm to
the apk name, for example (and w/ the zygote stuff cmdline isn't
really a thing)
I guess it could be drm-client-comm and drm-client-cmdline? Although
comm/cmdline aren't the best names, they are just following what the
kernel calls them elsewhere.
I wasn't sure what do you plan to do given mention of a path under the
drm-comm description. If it is a path then comm would be misleading,
since comm as defined in procfs is not a path, I don't think so at
least. Which is why I was suggesting executable. But if you remove the
mention of a path from rst and rather refer to processes' comm value I
think that is then okay.
+
+- drm-cmdline: <valstr>
+
+Returns the clients cmdline.
I think drm-usage-stats.rst text should provide some more text with
these two. To precisely define their content and outline the use case
under which driver authors may want to add them, and fdinfo consumer
therefore expect to see them. Just so everything is completely clear and
people do not start adding them for drivers which do not support native
context (or like).
I really was just piggy-backing on existing comm/cmdline.. but I'll
try to write up something better.
I think it maybe should not be limited just to native context.. for
ex. if the browser did somehow manage to create different displays
associated with different drm_file instances (I guess it would have to
use gbm to do this?) it would be nice to see browser tab names.
Would be cool yes.
My thinking behind why we maybe do not want to blanket add them is
because for common case is it the same information which can be obtained
from procfs. Like in igt_drm_clients.c I get the pid and comm from
/proc/$pid/stat. So I was thinking it is only interesting to add to
fdinfo for drivers where it could differ by the explicit override like
you have with native context.
It can be added once there is a GL/whatever extension which would allow
it? (I am not familiar with how browsers manage rendering contexts so
maybe I am missing something.)
But on the overall it sounds reasonable to me - it would be really cool
to not just see pcivirtio-gpu as you say. Even if the standard virtiogpu
use case (not native context) could show real users.
For vrend/virgl, we'd first need to solve the issue that there is just
a single drm_file for all guest processes. But really, just don't use
virgl. (I mean, like seriously, would you put a gl driver in the
kernel? Vrend has access to all guest memory, so this is essentially
what you have with virgl. This is just not a sane thing to do.) The
only "valid" reason for not doing native-context is if you don't have
the src code for your UMD to be able to modify it to talk
native-context to virtgpu in the guest. ;-)
I am just observing the current state of things on an Intel based
Chromebook. :) Presumably the custom name for a context would be
passable via the virtio-gpu protocol or something?
Regards,
Tvrtko
BR,
-R
Regards,
Tvrtko
+
Implementation Details
======================
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index f0f4f845c32d..1150dcbf28aa 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -148,12 +148,26 @@ int msm_gpu_pm_suspend(struct msm_gpu *gpu)
return 0;
}
+static void get_comm_cmdline(struct msm_file_private *ctx, char **comm, char **cmd);
+
void msm_gpu_show_fdinfo(struct msm_gpu *gpu, struct msm_file_private *ctx,
struct drm_printer *p)
{
+ char *comm, *cmdline;
+
+ get_comm_cmdline(ctx, &comm, &cmdline);
+
drm_printf(p, "drm-engine-gpu:\t%llu ns\n", ctx->elapsed_ns);
drm_printf(p, "drm-cycles-gpu:\t%llu\n", ctx->cycles);
drm_printf(p, "drm-maxfreq-gpu:\t%u Hz\n", gpu->fast_rate);
+
+ if (comm)
+ drm_printf(p, "drm-comm:\t%s\n", comm);
+ if (cmdline)
+ drm_printf(p, "drm-cmdline:\t%s\n", cmdline);
+
+ kfree(comm);
+ kfree(cmdline);
}
int msm_gpu_hw_init(struct msm_gpu *gpu)