Linux.conf.au 2017 – Thursday – Session 1

The Vulkan Graphics API, what it means for Linux – David Airlie

  • What is Vulkan
    • Not OpenGL++
    • From Scratch, Low Level, Open Graphics API
    • Stack
      • Loader (Mostly just picks the driver)
      • Layers (sometimes optional) – Seperate from the drivers.
        • Validation
        • Application Bug fixing
        • Tracing
        • Default GPU selection
      • Drivers (ICDs)
    • Open Source test Suite. ( “throw it over the wall Open Source”)
  • Why a new 3D API
    • OpenGL is old, from 1992
    • OpenGL Design based on 1992 hardware model
    • State machine has grown a lot as hardware has changed
    • Lots of stuff in it that nobody uses anymore
    • Some ideas were not so good in retrospec
      • Single context makes multi-threading hard
      • Sharing context is not reliable
      • Orientated around windows, off-screen rendering is a bolt-on
      • GPU hardware has converged to just 3-5 vendors with similar hardware. Not as much need to hid things
    •  Vulkan moves a lot of stuff up to the application (or more likely the OS graphics layer like Unity)
    • Vulkan gives applications access to the queues if they want them.
    • Shading Language – SPIR-V
      • Binary formatted, seperate from Vulkan, also used by OpenGL
      • Write Shaders HSL or GLSL and they get converted to SPIR-V
    • Driver Development
      • Almost all Error checking needed since done on the validation layer
      • Simpler to explicitly build command stream and then submit
    • Linux Support
      • Closed source Drivers
        • Nvidia
        • AMD (amdgpu-pro) – promised open source “real soon now … a year ago”
      • Open Source
        • Intel Linux (anv) –
          • on release day. 3.5 people over 8 months
          • SPIR -> NIR
          • Vulkan X11/Wayland WSI
          • anv Vulkan <– Core driver, not sharable
          • NIR -> i965 gen
          • ISL Library (image layout/tiling)
        • radv (for AMD GPUs)
          • Dave has been working on it since early July 2016 with one other guy
          • End of September Doom worked.
          • One Benchmark faster than AMD Driver
          • Valve hired someone to work on the driver.
          • Similar model to Intel anv driver.
          • Works on the few Vulkan games, working on SteamVR

 

Building reliable Ceph clusters – Lars Marowsky-Brée

  • Ceph
    • Storage Project
    • Multiple front ends (S3, Swift, Block IO, iSCSI, CephFS)
    • Built on RADOS data store
    • Software Defined Storage
      • Commodity servers + ceph + OS + Mngt (eg Open Attic)
      • Makes sense at 4+ servers with 10 drives each
      • metadata servce
      • CRUSH algorithm to speread out the data, no centralised table (client goes directly to data)
    • Access Methods
      • Use only what you need
      • RADOS Block devices   <– most stable
      • S3 (or Swift) via RadosGW  <– Mature
      • CephFS  <— New and pretty stable , avoid stuff non meta-data intensive
    • Introducing Dependability
      • Availability
      • Reliability
        • Duribility
      • Safety
      • Maintainability
    • Most outages are caused by Humans
    • At Scale everything fails
      • The Distributed systems are still vulnerable to correlated failures (eg same batch of hard drives)
      • Advantages of Heterogeneity – Everything is broken different
      • Homogeneity is non-sustainable
    • Failure is inevitable; suffering is optional
      • Prepare for downtime
      • Test if system meets your SLA when under load and when degraded and during recovery
    • How much available do you need?
      • An extra nine will double your price
  • A Bag full of suggestions
    • Embrace diversity
      • Auto recovery requires a >50% majority
      • 3 suppliers?
      • Mix arch and stuff between racks/pods and geography
      • Maybe you just go with manually added recovery
    • Hardware Choices
      • Vendors have reference archetectures
      • Hard to get vendors to mix, they don’t like that and fewer docs.
      • Hardware certification reduces the risk
      • Small variations can have huge impact
        • Customer bought network card and switch one up from the ref architecture. 6 months of problems till firmware bug fixed.
    • How many monitors do I need?
      • Not performance critcal
      • 3 is usually enough as long as well distributed
      • Big envs maybe 5 or 7
      • Don’t coverge (VMs) these with other types of nodes
    • Storage
      • Avoid Desktop Disks and SSDs
    • Storage Node sizing
      • A single node should not be more than 10% of your capacity
      • You need space capacity at least as big as a single node (to recover after fail)
    • Durability
      • Erasure Encode more durabily and high percentage of disk used
      • But recovery a lot slower, high overhead, etc
      • Different strokes for different pools
    • Network cards, different types, cross connect, use last years cards
    • Gateways: tests okay under failure
    • Config drift: Use config mngt (puppet etc)
    • Monioring
      • Perf as system ages
      • SSD degradation
    • Updates
      • Latest software is always the best
      • Usually good to update
      • Can do rolling upgrades
      • But still test a little on a staging server first
      • Always test on your system
        • Don’t trust metrics from vendors
        • Test updates
        • test your processes
        • Use OS to avoid vendor lock in
    • Disaster will strike
      • Have backups and test them and recoveries
    • Avoid Complexity
      • Be aggressive in what you test
      • Be commiserative in what you deploy only what you need
    • Q: Minimum size?
    • A: Not if you can fit on a single server