inside xbox one martin fuller xbox advanced technology group amd and microsoft game developer day -...

Inside Xbox One

Martin FullerXbox Advanced Technology Group

AMD AND MICROSOFT GAME DEVELOPER DAY - June 2 2014, STOCKHOLM

AMD AND MICROSOFT GAME DEVELOPER DAY - June 2 2014, STOCKHOLM 2

• This is a non-NDA event• That means there is a limit to how much I can say, go easy!

NDA


AMD Jaguar (x64) - 8-cores arranged in 2x clusters of 4 cores each

1.75 GHz

Dual issue

Out of order execution

Speculative execution

Store-to-load forwarding

SSE4.2 and AVX

(Dot product!)

16 x 256-bit wide floating point registers

Hardware pre-fetch

CPU


8 GiB of DDR3 at 68 GiB/s Low latency

Not enough bandwidth to touch all of memory a frame, RAM as a super fast cache

48-bit virtual address space 256 terabytes

Tricky to fragment!

Synced between CPU and GPU

4 MiB of L2 cache 2 MiB per cluster

MOESI protocol for cache coherency

16-way set associative

Per core, up to eight cache requests in flight at once

Memory


1. Store to load forwarding saves the dreaded LHS stall But not spilling out registers is even better

2. The branch predictor is not a crystal ball Branchless tricks learnt in Xbox 360 era can still apply

3. Hardware data pre-fetch is awesome Only works with arrays

4. Avoid aliasing load/stores on 2KiB alignments This causes a false positive that delays load execution

5. Go wide with SSE and leverage all cores No brainer

CPU – Recommendations


AMD GCN 768-SPU • 853 MHz

• 32 MiB of ESRAM at 109 GiB/s

• 4 Move Engines

• 3 hardware display planes

Resolution independent

Frame rate independent

• Exact sRGB this time!

(oh, and its free)

• Hardware video encode and decode

• HDMI 1.4a in and out

GPU


More than just DMA copy Memory set

Texture swizzle

JPEG decompress

LZ compress and decompress

Move Engines


32MiB of general purpose RAM Not like EDRAM on Xbox 360

109 GiB/s

Sometimes faster in practice!

Zero contention

Not shared with CPU, SRA’s or video out

ESRAM makes everything better

Render targets

Textures

Geometry

Compute tasks

ESRAM


ESRAM can handle concurrent read/writes:Increasing effective bandwidth above 109 GiB/s

Operations that can take advantage of this:1. Read modify write operations

1. Depth buffer / HTILE update

2. Alpha blending

2. Oh, and concurrently DMA’ing resources in/out of ESRAM while also rendering

How much effective bandwidth can titles achieve?3. The current record holder achieved 141 GiB/s from ESRAM (this is a post processing pass in

a real title)

4. Of course all titles combine ESRAM’s >= 109 GiB/s with DRAM’s 68 GiB/s

ESRAM – Sometimes faster in practice?


1. Statically allocate a small number of render targets in ESRAM

2. Alias the same memory for re-use later

3. Partial residency Put the top strip of render targets (sky) in DRAM, the rest in ESRAM

4. Asynchronously DMA resources in/out of ESRAM

Launch titles were at 1 - 2

2nd wave of titles are now starting to tackle points 3 and/or 4

3rd+ wave will get really good at this!

ESRAM – The Four Stages of Adoption


It’s like 8 bit days all over again!(Sort of)

Plan the asynchronous moves Move resources in/out asynchronous while also rendering

New memory map at each stage of the render pipeline

Don’t forget, swizzle textures on DMA

ESRAM – Memory Maps!


1. Are you bandwidth limited?

2. Have you maxed out the fixed function hardware?

3. Do you have spare compute resource?

Then use async compute!

Titles have barely scratched the surface yet:

Watch this space!

Maxing out the GPU


1. Use ESRAM First for depth / stencil

Then colour targets

Then everything else

2. Sort by state / shader / use hardware instancing (Batch batch batch!)

3. Always swizzle textures

4. Be wary of using too many general purpose registers Keep an eye on occupancy in PIX, we normally recommend >= 4

5. Avoid reading DRAM via the CPU-coherent bus

6. There is no hardware integer divide

The usual GPU recommendations


DX11 was designed for the desktop (a long time ago, 2008!) Abstracts a variety of different GPU architectures

Manages VRAM residency for you

Over subscribing VRAM is a serious performance pitfall

Handles hazards

Developers can handle these at a higher level => less cost

Xbox One will run vanilla DX11 PC code Easy port

Extensions available for low level access

Graphics API


DX11.X Some DX12 features available right now on Xbox:

Turn off hazard tracking

Simple fence API

Deferred contexts re-implemented

New resource descriptor model

Draw bundles

(Xbox specific, not the DX12 API)

Graphics API


The CPU cannot saturate DRAM bandwidth on its own, the GPU can! Significant performance degradation from DRAM contention

Fancy CPU features don’t help if memory starved

10. Use ESRAM as much as possible

20. Leave DRAM for the CPU and DMA

30. goto 10;

DRAM - Contention


1. Hardware data cache pre-fetch units are awesome Manual pre-fetch is near pointless once hardware pre-fetch is spinning

Wasting bandwidth if only operating on small arrays

2. Write combined memory pages and SSE streaming store instructions by-pass the cache

No load - halves the bandwidth consumed by the CPU

3. Pack your data! Expanding / compressing data is cheap (CPU & GPU)

F16C (half <-> float) CPU instructions

Store to load forwarding avoids LHS stalls

4. Swizzle your textures Move engines can swizzle on copy

DRAM – Love your bandwidth


Custom audio hardware Very fast

Lots of features

Kinda cool!

Nuff said

Audio


1. ERA Exclusive Resource Allocation

Only one active at a time

Custom OS

(Games!)

2. SRA Shared Resource Allocation

Win8 core

(Apps)

3. Hypervisor SRA and ERA use different virtual address space

3x Operating Systems


ERA can be in one of several states

1. Full screen Full resources (even with snapped app up)

2. Constrained (Windowed) Slightly less CPU and GPU resource

No input

Same amount of memory

3. Suspended Zero CPU and GPU resource

No input

Same amount of memory

Limited time to save after receiving a suspend message

PLM (Program Lifetime Management)


Hardware: Higher resolution colour and depth

Better ranges

New – infrared!

Microphone array

No tilt motor

Software: Improved skeletal tracking

Improved biometrics

Kinect 2.0


6x Bluray = ~26 MiB/s To install a 50 GiB Bluray at ~26 MiB/s = ~33 minutes

Too long to wait… bored now… Game must start after an initial payload has been installed.

When running title can hint as to what to install next.

No direct access to Bluray.

Could be digital download

It’s obvious but I’ll say it anyway – compress you assets!

Streaming install


Cloud compute:• Developer’s code is hosted and executed in Windows Azure

• Game code execution automatically scales based upon usage

Live services:• Stats, analytics, matchmaking & storage.

Secure!

The Cloud


1. Is your code 64-bit compliant?

2. Can you scale to 6 cores?

3. Adopt new DX11.X API extensions Manage your own resource hazards

4. Make sure you use ESRAM effectively

5. Package content for streaming install Game design considerations

6. Quick save on ERA termination

7. Kinect, Smartglass

8. Cloud services

Challenges


(That I’m allowed to answer)

Thank You! – Questions?

© 2014 Microsoft

The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing

market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation.

Microsoft makes no warranties, express, implied or statutory, as to the information in this presentation.

inside xbox one martin fuller xbox advanced technology group amd and microsoft game developer day -...

Documents

microsoft game developer

stockholm slide

memory slide

gibs esram

gpu slide

amd gcn

mib of esram

nda slide