Re: [PATCH v4] drm/amdgpu: add new trace event for page table update v3

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Am 19.08.20 um 15:08 schrieb Shashank Sharma:
On 19/08/20 6:34 pm, Christian König wrote:
Am 19.08.20 um 14:37 schrieb Shashank Sharma:
On 19/08/20 6:03 pm, Christian König wrote:
Am 19.08.20 um 14:19 schrieb Shashank Sharma:
On 19/08/20 5:38 pm, Christian König wrote:
Am 19.08.20 um 13:52 schrieb Shashank Sharma:
On 13/08/20 1:28 pm, Christian König wrote:
Am 13.08.20 um 05:04 schrieb Shashank Sharma:
This patch adds a new trace event to track the PTE update
events. This specific event will provide information like:
- start and end of virtual memory mapping
- HW engine flags for the map
- physical address for mapping

This will be particularly useful for memory profiling tools
(like RMV) which are monitoring the page table update events.

V2: Added physical address lookup logic in trace point
V3: switch to use __dynamic_array
         added nptes int the TPprint arguments list
         added page size in the arg list
V4: Addressed Christian's review comments
         add start/end instead of seg
         use incr instead of page_sz to be accurate

Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxx>
---
      drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h | 37 +++++++++++++++++++++++
      drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  9 ++++--
      2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h
index 63e734a125fb..df12cf8466c2 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h
@@ -321,6 +321,43 @@ DEFINE_EVENT(amdgpu_vm_mapping, amdgpu_vm_bo_cs,
      	    TP_ARGS(mapping)
      );
+TRACE_EVENT(amdgpu_vm_update_ptes,
+	    TP_PROTO(struct amdgpu_vm_update_params *p,
+		     uint64_t start, uint64_t end,
+		     unsigned int nptes, uint64_t dst,
+		     uint64_t incr, uint64_t flags),
+	TP_ARGS(p, start, end, nptes, dst, incr, flags),
+	TP_STRUCT__entry(
+			 __field(u64, start)
+			 __field(u64, end)
+			 __field(u64, flags)
+			 __field(unsigned int, nptes)
+			 __field(u64, incr)
+			 __dynamic_array(u64, dst, nptes)
As discussed with the trace subsystem maintainer we need to add the pid
and probably the VM context ID we use here to identify the updated VM.

Christian.
I printed both vm->task_info.pid Vs current->pid for testing, and I can see different values coming out of .

gnome-shell-2114  [011]    41.812894: amdgpu_vm_update_ptes: start:0x0800102e80 end:0x0800102e82, flags:0x80, incr:4096, pid=2128 vmid=0 cpid=2114

pid is vm->task_info.pid=2128 whereas cpid=2114 is current.pid.

Which is the one we want to send with the event ?
That is vm->task_info.pid, since this is the PID which is using the VM
for command submission.
got it.
Trace event by default seems to be adding the process name and id at the header of the event (gnome-shell-2114), which is same as current.pid


Also, is it ok to extract vmid from job->vmid ?
Only in trace_amdgpu_vm_grab_id(), in all other cases it's probably not
assigned yet.
Ok, let me check how can we get vmid from this context we are sending the event from. Or maybe I we should  keep V5 with pid only, and later send a separate patch to add vmid ?
I'm not sure how you want to get a VMID in the first place. We
dynamically assign VMIDs during command submission.

See the amdgpu_vm_grab_id trace point.
Actually I was adding vmid to address this last comment on V4:
and probably the VM context ID we use here to identify the updated VM.
I assumed you meant the vmid by this, is that not so ?
Ah! No that's something completely different :)

The VMID is a 4bit hardware identifier used for TLB optimization.

The VM context ID is an unique 64bit number, we usually use
vm->immediate.fence_context for this.
Damn, why is it never what you hope it to be :). Thanks for this information, I will check this out first.

Multiple reasons :)

One is that I'm not a native speaker of English and only had very limited formal education in the language :)

Another one is that the hardware and driver is rather complicated.

Regards,
Christian.
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