Tools for Investigating Graphics
System Performance
Matthew Fisher
Steve Pronovost
Goal
A video game runs slowly, skips frames, has
high latency, etc. and the developers want to
fix this problem
 The problem is almost always a cascade of
bottlenecks at the application, CPU, and GPU
levels that is very challenging to investigate
locally
 We want tools that lets programmers solve
these problems faster

Approaches

Profiling
– Rig the game events with logging or use an
automatic profiler

PIX (for Windows and Xbox 360)
– All calls by the game to the graphics API are
logged

GPUView
– OS logs all CPU, graphics kernel and graphics
driver events
Profiling
Manual profiling requires a significant amount
of development effort
 Polling-based automatic profiling can work
reasonably well for CPU applications but
doesn’t capture graphics or memory transfer
events well
 Percentage-based statistics (“you spent 45% of
the time in function X”) can sometimes be
useful and sometimes extremely misleading

PIX
Released by Microsoft as part of the DirectX
SDK
 Multiple modes for investigating performance
targeted at game developers

– Interactive mode
– Frame logging
– Frame capture and playback
PIX – Interactive Mode
Various counters stream by as the game runs
 You can change the counters, hope is to find
that the observed problem correlates with
one of the counters

PIX – Interactive Mode
Commonly Used Counter Types
Number, type, and size of draw primitive calls
 Number of texture, vertex/index buffer locks,
and what memory pool was locked
 Object creation and destruction events
 Allocated system and video memory
 Frame latency, seconds per frame
 Page faults

PIX – Frame Capture Mode
PIX – Debug Pixel
Questions PIX is good at
Are object locks causing the frame skipping
problem users are experiencing?
 Are we allocating too many resources we
don’t use?
 What are the API calls that are taking the
longest time to execute?
 Why was this pixel in the sky green?

GPUView
Windows Display Driver Model
The XP Display Driver Model required
applications to cede control of the graphics
infrastructure and was largely designed
assuming a single 3D application would be
running
 The Vista Display Driver Model added
standard scheduling principles forcing
applications to share control of graphics
memory and compute resources

GPUView
The graphics model switch induced a variety
of constraints on graphics applications and
forced highly optimized graphics drivers to be
restructured
 Many games were running more slowly on
Vista than they did on XP (~5% - 30% slower)
 GPUView was designed to help investigate
these problems and see what stage was
causing the speed difference

Event Tracing

The GPUView logger enables logging of a vast
set of events in the OS, such as
– All calls to the Windows graphics kernel
• All resource creation, lock, destruction, etc. events
• All command buffer submissions
– Context switches (w/ stack trace and reason)
– Kernel mode enter/exits (w/ stack trace)

World of Warcraft generates approximately
1GB every 3 seconds
GPUView Without Any Graphics
Windows Display Driver Model
Applications build up local command buffers
 When these command buffers get big enough
they are submitted to the application’s local
graphics queue for processing
 The graphics scheduler selects which
application should be running on which
graphics card and submits work to the
corresponding hardware queue

One Second of a Game
Setup
Multiple Applications Fighting
Simple Problems
Relatively Normal Execution
GPU Starvation
GPU Idle
Sleepy App
Huge Render Times (GPU Bound)
GPU and CPU Starvation
Answering Questions
Why Did Our Thread Context Switch?
Does Surface Allocation Cause Frame Stuttering?
Thoughts
Surprisingly, the overhead of GPUView logging
is pretty minimal and the traces often reflect
the underlying problem well
 The biggest advantage of GPUView over PIX is
that PIX can’t tell you crucial things like when
the GPU is blocked on the CPU
 GPUView is excellent for telling you what part
of the application needs optimization

Driver Perspective

Provides a lot of detail to let display driver
writers and the DirectX graphics kernel
diagnose problems with task submission, the
command buffer submission threads, GPU
preemption, video skipping, etc.