Computers for the Post-PC Era

1
Computers for the Post-PC Era

• David Patterson
• University of California at Berkeley
• Patterson_at_cs.berkeley.edu
• UC Berkeley IRAM Group
• UC Berkeley ISTORE Group
• istore-group_at_cs.berkeley.edu
• February 2000

2
Perspective on Post-PC Era

• PostPC Era will be driven by 2 technologies
• 1) GadgetsTiny Embedded or Mobile Devices
• ubiquitous in everything
• e.g., successor to PDA, cell phone, wearable
  computers
• 2) Infrastructure to Support such Devices
• e.g., successor to Big Fat Web Servers, Database
  Servers

3
Outline

• 1) Example microprocessor for PostPC gadgets
• 2) Motivation and the ISTORE project vision
• AME Availability, Maintainability, Evolutionary
  growth
• ISTOREs research principles
• Proposed techniques for achieving AME
• Benchmarks for AME
• Conclusions and future work

4
Intelligent RAM IRAM

• Microprocessor DRAM on a single chip
• 10X capacity vs. SRAM
• on-chip memory latency 5-10X, bandwidth 50-100X
• improve energy efficiency 2X-4X (no off-chip
  bus)
• serial I/O 5-10X v. buses
• smaller board area/volume
• IRAM advantages extend to
• a single chip system
• a building block for larger systems

5
Revive Vector Architecture

• Single-chip CMOS MPU/IRAM
• IRAM
• Much smaller than VLIW
• For sale, mature (gt20 years)(We retarget Cray
  compilers)
• Easy scale speed with technology
• Parallel to save energy, keep perf
• Multimedia apps vectorizable too N64b, 2N32b,
  4N16b

• Cost 1M each?
• Low latency, high BW memory system?
• Code density?
• Compilers?
• Performance?
• Power/Energy?
• Limited to scientific applications?

6
V-IRAM1 Low Power v. High Perf.

4 x 64 or 8 x 32 or 16 x 16
x
2-way Superscalar
Vector
Instruction

Processor
Queue
Load/Store
Vector Registers
16K I cache
16K D cache
4 x 64
4 x 64
Serial I/O
Memory Crossbar Switch
M
M
M
M
M
M
M
M
M
M

M
M
M
M
M
M
M
M
M
M
4 x 64
4 x 64
4 x 64
4 x 64
4 x 64










M
M
M
M
M
M
M
M
M
M
7
VIRAM-1 System on a Chip

• Prototype scheduled for tape-out mid 2000
• 0.18 um EDL process
• 16 MB DRAM, 8 banks
• MIPS Scalar core and
  caches _at_ 200 MHz
• 4 64-bit vector unit
  pipelines _at_ 200 MHz
• 4 100 MB parallel I/O lines
• 17x17 mm, 2 Watts
• 25.6 GB/s memory (6.4 GB/s per direction
  and per Xbar)
• 1.6 Gflops (64-bit), 6.4 GOPs (16-bit)

Memory (64 Mbits / 8 MBytes)
Xbar
I/O
Memory (64 Mbits / 8 MBytes)
8
Media Kernel Performance
9
Base-line system comparison

• All numbers in cycles/pixel
• MMX and VIS results assume all data in L1 cache

10
IRAM Chip Challenges

• Merged Logic-DRAM process Cost Cost of wafer,
  Impact on yield, testing cost of logic and DRAM
• Price on-chip DRAM v. separate DRAM chips?
• Delay in transistor speeds, memory cell sizes in
  Merged process vs. Logic only or DRAM only
• DRAM block flexibility via DRAM compiler (vary
  size, width, no. subbanks) vs. fixed block
• Apps advantages in memory bandwidth, energy,
  system size to offset challenges?

11
Other examples IBM Blue Gene

• 1 PetaFLOPS in 2005 for 100M?
• Application Protein Folding
• Blue Gene Chip
• 32 Multithreaded RISC processors ??MB Embedded
  DRAM high speed Network Interface on single 20
  x 20 mm chip
• 1 GFLOPS / processor
• 2 x 2 Board 64 chips (2K CPUs)
• Rack 8 Boards (512 chips,16K CPUs)
• System 64 Racks (512 boards,32K chips,1M CPUs)
• Total 1 million processors in just 2000 sq. ft.

12
Other examples Sony Playstation 2

• Emotion Engine 6.2 GFLOPS, 75 million polygons
  per second (Microprocessor Report, 135)
• Superscalar MIPS core vector coprocessor
  graphics/DRAM
• Claim Toy Story realism brought to games

13
Outline

• 1) Example microprocessor for PostPC gadgets
• 2) Motivation and the ISTORE project vision
• AME Availability, Maintainability, Evolutionary
  growth
• ISTOREs research principles
• Proposed techniques for achieving AME
• Benchmarks for AME
• Conclusions and future work

14
The problem space big data

• Big demand for enormous amounts of data
• today high-end enterprise and Internet
  applications
• enterprise decision-support, data mining
  databases
• online applications e-commerce, mail, web,
  archives
• future infrastructure services, richer data
• computational storage back-ends for mobile
  devices
• more multimedia content
• more use of historical data to provide better
  services
• Todays SMP server designs cant easily scale to
  meet these huge demands

15
One approach traditional NAS

• Network-attached storage makes storage devices
  first-class citizens on the network
• network file server appliances (NetApp, SNAP,
  ...)
• storage-area networks (CMU NASD, NSIC OOD, ...)
• active disks (CMU, UCSB, Berkeley IDISK)
• These approaches primarily target performance
  scalability
• scalable networks remove bus bandwidth
  limitations
• migration of layout functionality to storage
  devices removes overhead of intermediate servers
• There are bigger scaling problems than scalable
  performance!

16
The real scalability problems AME

• Availability
• systems should continue to meet quality of
  service goals despite hardware and software
  failures
• Maintainability
• systems should require only minimal ongoing human
  administration, regardless of scale or complexity
• Evolutionary Growth
• systems should evolve gracefully in terms of
  performance, maintainability, and availability as
  they are grown/upgraded/expanded
• These are problems at todays scales, and will
  only get worse as systems grow

17
The ISTORE project vision

• Our goal
• develop principles and investigate hardware/sof
  tware techniques for building storage-based
  server systems that
• are highly available
• require minimal maintenance
• robustly handle evolutionary growth
• are scalable to O(10000) nodes

18
Principles for achieving AME (1)

• No single points of failure
• Redundancy everywhere
• Performance robustness is more important than
  peak performance
• performance robustness implies that real-world
  performance is comparable to best-case
  performance
• Performance can be sacrificed for improvements in
  AME
• resources should be dedicated to AME
• compare biological systems spend gt 50 of
  resources on maintenance
• can make up performance by scaling system

19
Principles for achieving AME (2)

• Introspection
• reactive techniques to detect and adapt to
  failures, workload variations, and system
  evolution
• proactive techniques to anticipate and avert
  problems before they happen

20
Outline

• 1) Example microprocessor for PostPC gadgets
• 2) Motivation and the ISTORE project vision
• AME Availability, Maintainability, Evolutionary
  growth
• ISTOREs research principles
• Proposed techniques for achieving AME
• Benchmarks for AME
• Conclusions and future work

21
Hardware techniques

• Fully shared-nothing cluster organization
• truly scalable architecture
• architecture that tolerates partial failure
• automatic hardware redundancy
• No Central Processor Unit distribute processing
  with storage
• if AME is important, must provide resources to be
  used for AME
• Nodes responsible for health of their storage
• Serial lines, switches also growing with Moores
  Law less need today to centralize vs. bus
  oriented systems

22
Hardware techniques (2)

• Heavily instrumented hardware
• sensors for temp, vibration, humidity, power,
  intrusion
• helps detect environmental problems before they
  can affect system integrity
• Independent diagnostic processor on each node
• provides remote control of power, remote console
  access to the node, selection of node boot code
• collects, stores, processes environmental data
  for abnormalities
• non-volatile flight recorder functionality
• all diagnostic processors connected via
  independent diagnostic network

23
Hardware techniques (3)

• On-demand network partitioning/isolation
• Allows testing, repair of online system
• managed by diagnostic processor and network
  switches via diagnostic network
• Built-in fault injection capabilities
• power control to individual node components
• injectable glitches into I/O and memory busses
• managed by diagnostic processor
• used for proactive hardware introspection
• automated detection of flaky components
• controlled testing of error-recovery mechanisms
• important for AME benchmarking

24
Hardware techniques (4)

• Benchmarking
• One reason for 1000X processor performance was
  ability to measure (vs. debate) which is better
• e.g., Which most important to imrpove clock
  rate, clocks per instruction, or instructions
  executed?
• Need AME benchmarks
• what gets measured gets done
• benchmarks shape a field
• quantification brings rigor

25
ISTORE-1 hardware platform

• 80-node x86-based cluster, 1.4TB storage
• cluster nodes are plug-and-play, intelligent,
  network-attached storage bricks
• a single field-replaceable unit to simplify
  maintenance
• each node is a full x86 PC w/256MB DRAM, 18GB
  disk
• more CPU than NAS fewer disks/node than cluster

Intelligent Disk Brick Portable PC CPU Pentium
II/266 DRAM Redundant NICs (4 100 Mb/s
links) Diagnostic Processor

• ISTORE Chassis
• 80 nodes, 8 per tray
• 2 levels of switches
• 20 100 Mb/s
• 2 1 Gb/s
• Environment Monitoring
• UPS, redundant PS,
• fans, heat and vibration sensors...

26
ISTORE Brick Block Diagram
Mobile Pentium II Module
SCSI
North Bridge
CPU
Disk (18 GB)
South Bridge
Diagnostic Net
DUAL UART
DRAM 256 MB
Super I/O
Monitor Control
Diagnostic Processor
BIOS
Ethernets 4x100 Mb/s
PCI

• Sensors for heat and vibration
• Control over power to individual nodes

Flash
RTC
RAM
27
A glimpse into the future?

• System-on-a-chip enables computer, memory,
  redundant network interfaces without
  significantly increasing size of disk
• ISTORE HW in 5-7 years

• building block 2006 MicroDrive integrated with
  IRAM
• 9GB disk, 50 MB/sec from disk
• connected via crossbar switch
• 10,000 nodes fit into one rack!
• O(10,000) scale is our ultimate design point

28
Software techniques

• Fully-distributed, shared-nothing code
• centralization breaks as systems scale up
  O(10000)
• avoids single-point-of-failure front ends
• Redundant data storage
• required for high availability, simplifies
  self-testing
• replication at the level of application objects
• application can control consistency policy
• more opportunity for data placement optimization

29
Software techniques (2)

• River storage interfaces
• NOW Sort experience performance heterogeneity
  is the norm
• e.g., disks outer vs. inner track (1.5X),
  fragmentation
• e.g., processors load (1.5-5x)
• So demand-driven delivery of data to apps
• via distributed queues and graduated declustering
• for apps that can handle unordered data delivery
• automatically adapts to variations in performance
  of producers and consumers

30
Software techniques (3)

• Reactive introspection
• use statistical techniques to identify normal
  behavior and detect deviations from it
• policy-driven automatic adaptation to abnormal
  behavior once detected
• initially, rely on human administrator to specify
  policy
• eventually, system learns to solve problems on
  its own by experimenting on isolated subsets of
  the nodes
• one candidate reinforcement learning

31
Software techniques (4)

• Proactive introspection
• continuous online self-testing of HW and SW
• in deployed systems!
• goal is to shake out Heisenbugs before theyre
  encountered in normal operation
• needs data redundancy, node isolation, fault
  injection
• techniques
• fault injection triggering hardware and software
  error handling paths to verify their
  integrity/existence
• stress testing push HW/SW to their limits
• scrubbing periodic restoration of potentially
  decaying hardware or software state
• self-scrubbing data structures (like MVS)
• ECC scrubbing for disks and memory

32
Applications

• ISTORE is not one super-system that demonstrates
  all these techniques!
• Initially provide library to support AME goals
• Initial application targets
• cluster web/email servers
• self-scrubbing data structures, online
  self-testing
• statistical identification of normal behavior
• decision-support database query execution system
• River-based storage, replica management
• information retrieval for multimedia data
• self-scrubbing data structures, structuring
  performance-robust distributed computation

33
Outline

• 1) Example microprocessor for PostPC gadgets
• 2) Motivation and the ISTORE project vision
• AME Availability, Maintainability, Evolutionary
  growth
• ISTOREs research principles
• Proposed techniques for achieving AME
• Benchmarks for AME
• Conclusions and future work

34
Availability benchmarks

• Questions to answer
• what factors affect the quality of service
  delivered by the system, and by how much/how
  long?
• how well can systems survive typical failure
  scenarios?
• Availability metrics
• traditionally, percentage of time system is up
• time-averaged, binary view of system state
  (up/down)
• traditional metric is too inflexible
• doesnt capture spectrum of degraded states
• time-averaging discards important temporal
  behavior

• Solution measure variation in system quality of
  service metrics over time
• performance, fault-tolerance, completeness,
  accuracy

35
Availability benchmark methodology

• Goal quantify variation in QoS metrics as events
  occur that affect system availability
• Leverage existing performance benchmarks
• to generate fair workloads
• to measure trace quality of service metrics
• Use fault injection to compromise system
• hardware faults (disk, memory, network, power)
• software faults (corrupt input, driver error
  returns)
• maintenance events (repairs, SW/HW upgrades)
• Examine single-fault and multi-fault workloads
• the availability analogues of performance micro-
  and macro-benchmarks

36
Methodology reporting results

• Results are most accessible graphically
• plot change in QoS metrics over time
• compare to normal behavior?
• 99 confidence intervals calculated from no-fault
  runs

• Graphs can be distilled into numbers?

37
Example results software RAID-5

• Test systems Linux/Apache and Win2000/IIS
• SpecWeb 99 to measure hits/second as QoS metric
• fault injection at disks based on empirical fault
  data
• transient, correctable, uncorrectable, timeout
  faults
• 15 single-fault workloads injected per system
• only 4 distinct behaviors observed
• (A) no effect (C) RAID enters degraded mode
• (B) system hangs (D) RAID enters degraded mode
  starts
  reconstruction
• both systems hung (B) on simulated disk hangs
• Linux exhibited (D) on all other errors
• Windows exhibited (A) on transient errors and (C)
  on uncorrectable, sticky errors

38
Example results multiple-faults
Windows 2000/IIS
Linux/ Apache

• Windows reconstructs 3x faster than Linux
• Windows reconstruction noticeably affects
  application performance, while Linux
  reconstruction does not

39
Conclusions (1) Benchmarks

• Linux and Windows take opposite approaches to
  managing benign and transient faults
• Linux is paranoid and stops using a disk on any
  error
• Windows ignores most benign/transient faults
• Windows is more robust except when disk is truly
  failing
• Linux and Windows have different reconstruction
  philosophies
• Linux uses idle bandwidth for reconstruction
• Windows steals app. bandwidth for reconstruction
• Windows rebuilds fault-tolerance more quickly
• Win2k favors fault-tolerance over performance
  Linux favors performance over fault-tolerance

40
Conclusions (2) ISTORE

• Availability, Maintainability, and Evolutionary
  growth are key challenges for server systems
• more important even than performance
• ISTORE is investigating ways to bring AME to
  large-scale, storage-intensive servers
• via clusters of network-attached,
  computationally-enhanced storage nodes running
  distributed code
• via hardware and software introspection
• we are currently performing application studies
  to investigate and compare techniques
• Availability benchmarks a powerful tool?
• revealed undocumented design decisions affecting
  SW RAID availability on Linux and Windows 2000

41
Conclusions (3)

• IRAM attractive for two Post-PC applications
  because of low power, small size, high memory
  bandwidth
• Gadgets Embedded/Mobile devices
• Scaleable infrastructure
• ISTORE hardware/software architecture for large
  scale network services
• PostPC infrastructure requires
• new goals Availability/Maintainability/Evolution
  
• new principles Introspection, Performance
  Robustness
• new techniques Isolation/fault insertion, SW
  scrubbing

42
Future work

• IRAM fab and test chip
• ISTORE
• implement AME-enhancing techniques in a variety
  of Internet, enterprise, and info retrieval
  applications
• select the best techniques and integrate into a
  generic runtime system with AME API
• add maintainability benchmarks
• can we quantify administrative work needed to
  maintain a certain level of availability?
• Perhaps look at data security via encryption?
• Consider denial of service? (or a job for IATF?)

43
The UC Berkeley IRAM/ISTORE ProjectsComputers
for the PostPC Era

• For more information
• http//iram.cs.berkeley.edu/istore
• istore-group_at_cs.berkeley.edu

44
Backup Slides

• (mostly in the area of benchmarking)

45
Case study

• Software RAID-5 plus web server
• Linux/Apache vs. Windows 2000/IIS
• Why software RAID?
• well-defined availability guarantees
• RAID-5 volume should tolerate a single disk
  failure
• reduced performance (degraded mode) after failure
• may automatically rebuild redundancy onto spare
  disk
• simple system
• easy to inject storage faults
• Why web server?
• an application with measurable QoS metrics that
  depend on RAID availability and performance

46
Benchmark environment metrics

• QoS metrics measured
• hits per second
• roughly tracks response time in our experiments
• degree of fault tolerance in storage system
• Workload generator and data collector
• SpecWeb99 web benchmark
• simulates realistic high-volume user load
• mostly static read-only workload some dynamic
  content
• modified to run continuously and to measure
  average hits per second over each 2-minute
  interval

47
Benchmark environment faults

• Focus on faults in the storage system (disks)
• How do disks fail?
• according to Tertiary Disk project, failures
  include
• recovered media errors
• uncorrectable write failures
• hardware errors (e.g., diagnostic failures)
• SCSI timeouts
• SCSI parity errors
• note no head crashes, no fail-stop failures

48
Disk fault injection technique

• To inject reproducible failures, we replaced one
  disk in the RAID with an emulated disk
• a PC that appears as a disk on the SCSI bus
• I/O requests processed in software, reflected to
  local disk
• fault injection performed by altering SCSI
  command processing in the emulation software
• Types of emulated faults
• media errors (transient, correctable,
  uncorrectable)
• hardware errors (firmware, mechanical)
• parity errors
• power failures
• disk hangs/timeouts

49
System configuration

• RAID-5 Volume 3GB capacity, 1GB used per disk
• 3 physical disks, 1 emulated disk, 1 emulated
  spare disk
• 2 web clients connected via 100Mb switched
  Ethernet

50
Results single-fault experiments

• One expt for each type of fault (15 total)
• only one fault injected per experiment
• no human intervention
• system allowed to continue until stabilized or
  crashed
• Four distinct system behaviors observed
• (A) no effect system ignores fault
• (B) RAID system enters degraded mode
• (C) RAID system begins reconstruction onto spare
  disk
• (D) system failure (hang or crash)

51
System behavior single-fault
(A) no effect
(B) enter degraded mode
(D) system failure
(C) begin reconstruction
52
System behavior single-fault (2)

• Windows ignores benign faults
• Windows cant automatically rebuild
• Linux reconstructs on all errors
• Both systems fail when disk hangs

53
Interpretation single-fault expts

• Linux and Windows take opposite approaches to
  managing benign and transient faults
• these faults do not necessarily imply a failing
  disk
• Tertiary Disk 368/368 disks had transient SCSI
  errors 13/368 disks had transient hardware
  errors, only 2/368 needed replacing.
• Linux is paranoid and stops using a disk on any
  error
• fragile system is more vulnerable to multiple
  faults
• but no chance of slowly-failing disk impacting
  perf.
• Windows ignores most benign/transient faults
• robust less likely to lose data, more
  disk-efficient
• less likely to catch slowly-failing disks and
  remove them
• Neither policy is ideal!
• need a hybrid?

54
Results multiple-fault experiments

• Scenario
• (1) disk fails
• (2) data is reconstructed onto spare
• (3) spare fails
• (4) administrator replaces both failed disks
• (5) data is reconstructed onto new disks
• Requires human intervention
• to initiate reconstruction on Windows 2000
• simulate 6 minute sysadmin response time
• to replace disks
• simulate 90 seconds of time to replace hot-swap
  disks

55
Interpretation multi-fault expts

• Linux and Windows have different reconstruction
  philosophies
• Linux uses idle bandwidth for reconstruction
• little impact on application performance
• increases length of time system is vulnerable to
  faults
• Windows steals app. bandwidth for reconstruction
• reduces application performance
• minimizes system vulnerability
• but must be manually initiated (or scripted)
• Windows favors fault-tolerance over performance
  Linux favors performance over fault-tolerance
• the same design philosophies seen in the
  single-fault experiments

56
Maintainability Observations

• Scenario administrator accidentally removes and
  replaces live disk in degraded mode
• double failure no guarantee on data integrity
• theoretically, can recover if writes are queued
• Windows recovers, but loses active writes
• journalling NTFS is not corrupted
• all data not being actively written is intact
• Linux will not allow removed disk to be
  reintegrated
• total loss of all data on RAID volume!

57
Maintainability Observations (2)

• Scenario administrator adds a new spare
• a common task that can be done with hot-swap
  drive trays
• Linux requires a reboot for the disk to be
  recognized
• Windows can dynamically detect the new disk
• Windows 2000 RAID is easier to maintain
• easier GUI configuration
• more flexible in adding disks
• SCSI rescan and NTFS deal with administrator
  goofs
• less likely to require administration due to
  transient errors
• BUT must manually initiate reconstruction when
  needed