Linux Foundation Collaboration Summit 2010 LTTng, State of the - - PowerPoint PPT Presentation

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Linux Foundation Collaboration Summit 2010 LTTng, State of the - - PowerPoint PPT Presentation

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Linux Foundation Collaboration Summit 2010 LTTng, State of the Union Presentation at: http://www.efficios.com/lfcs2010 E-mail: mathieu.desnoyers@efficios.com Mathieu Desnoyers April 15th, 2010 1 > Presenter Mathieu Desnoyers

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April 15th, 2010 Mathieu Desnoyers 1

Linux Foundation Collaboration Summit 2010

LTTng, State of the Union Presentation at: http://www.efficios.com/lfcs2010 E-mail: mathieu.desnoyers@efficios.com

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April 15th, 2010 Mathieu Desnoyers 2

> Presenter

  • Mathieu Desnoyers
  • EfficiOS Inc.
  • http://www.efficios.com
  • Author/Maintainer of
  • LTTng, LTTV, Userspace RCU
  • Ph.D. in computer engineering
  • Low-Impact Operating System Tracing
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April 15th, 2010 Mathieu Desnoyers 3

> Plan

  • Current state of LTTng
  • State of kernel tracing in Linux
  • User requirements
  • Vertical vs Horizontal integration
  • LTTng roadmap for 2010
  • Conclusion
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April 15th, 2010 Mathieu Desnoyers 4

> Current status of LTTng

  • LTTng dual-licensing: GPLv2/LGPLv2.1
  • UST user-space tracer

– Userspace RCU (LGPLv2.1)

  • Eclipse Linux Tools Project LTTng Integration
  • User-space static tracepoint integration with

gdb

  • LTTng kernel tracer

– maintainance-mode in 2009 (finished my Ph.D.) – active development restarting in 2010

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April 15th, 2010 Mathieu Desnoyers 5

> LTTng dual-licensing GPLv2/LGPLv2.1

  • LGPLv2.1 license is required to share code with

user-space tracer library.

  • License chosen to allow tracing of non-GPL

applications.

  • Headers are licensed under BSD:

– Demonstrates that these headers can be

included in non-GPL code.

  • Applies to:

– LTTng, Tracepoints, Kernel Markers, Immediate

Values

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April 15th, 2010 Mathieu Desnoyers 6

> User-space Tracing (UST) (1)

  • LTTng port to user-space
  • Re-uses Tracepoints and LTTng ring buffer
  • Uses Userspace RCU for control synchronization
  • Shared memory map with consumer daemon
  • Per-process per-cpu ring buffers
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April 15th, 2010 Mathieu Desnoyers 7

> User-space Tracing (UST) (2)

  • The road ahead

– Userspace trace clock for more architectures

  • Some require Linux kernel vDSO support for

trace clock

– Utrace

  • Provide information about thread creation, exec(),

etc...

  • Current alternative: overload library symbols
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April 15th, 2010 Mathieu Desnoyers 8

> Userspace RCU

  • Licensed under LGPLv2.1 since May 9 2009,

with IBM grant use of RCU patent.

  • Supports

– x86 (i386, i486, i586, i686) – x86 64-bit – PowerPC 32/64 – S390, S390x – Sparcv9 32/64 – Alpha and ia64 (with gcc 4.x atomic builtins)

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April 15th, 2010 Mathieu Desnoyers 9

> sys_membarrier()

  • Useful to Userspace RCU
  • Asymmetric distribution of memory barrier cost

using IPIs

– Lightweight reader synchronization

  • Currently x86, more architectures to come
  • State: submitted
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April 15th, 2010 Mathieu Desnoyers 10

> State of kernel tracing in Linux

  • Instrumentation
  • Tracers
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April 15th, 2010 Mathieu Desnoyers 11

> State of Linux instrumentation

  • Things are going very well

– Tracepoints

  • Many subsystems instrumented
  • System call instrumentation

– TRACE_EVENT() – Dynamic Probes – Function Tracer – Performance Counters

  • Interoperability
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April 15th, 2010 Mathieu Desnoyers 12

> State of Linux tracers

  • Ftrace, Perf

– Opening the Linux kernel developer community

to tracing

– Centered on kernel developers requirements – Still missing the point for companies developing

  • n top of Linux (end users)
  • Telecommunication companies
  • Embedded systems
  • Enterprise servers
  • And many many more .......................................
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April 15th, 2010 Mathieu Desnoyers 13

> User requirements (1)

Reflects the needs of the following users:

– Wind River – Monta Vista – Autodesk – Cisco – Mentor Graphics – Texas Instruments – Google – IBM – Ericsson – Nokia – Siemens – Freescale

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April 15th, 2010 Mathieu Desnoyers 14

> User requirements (2)

  • Compactness of traces
  • Scalability to multi-core and multi-processor
  • Low-overhead is key
  • Production-grade tracer reliability
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April 15th, 2010 Mathieu Desnoyers 15

> User requirements (3)

  • Heterogeneous environment support

– Portability – Distinct host/target environment support – Management of multiple target kernel versions – No dependency on kernel image to analyze

traces (traces contain complete information)

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April 15th, 2010 Mathieu Desnoyers 16

> User requirements (4)

  • Network streaming support
  • Live view/analysis of trace streams
  • System-wide (kernel and user-space) traces
  • Scalability of analysis tools to very large data

sets

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April 15th, 2010 Mathieu Desnoyers 17

> Vertical vs Horizontal integration

  • Vertical code integration

– Changes the core kernel – Kernel-wide impact – Infrastructure must be common and shared – Requires piecewise integration – e.g. instrumentation, trace clock

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April 15th, 2010 Mathieu Desnoyers 18

> Vertical vs Horizontal integration

  • Horizontal integration

– Stand-alone "driver" code – Localized impact – Infrastructure can be common and shared, but

not necessarily

– Factoring out and merging duplicated features

can be done as needed, incrementally

– e.g. tracer core

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April 15th, 2010 Mathieu Desnoyers 19

> LTTng tracer core

  • Trace Session Management
  • Information Channels Management
  • Wait-Free Ring Buffer
  • Ring Buffer Allocation
  • Data Transport with splice()
  • Kernel API
  • Userspace Interface (debugfs)
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April 15th, 2010 Mathieu Desnoyers 20

> LTTng roadmap for 2010

  • Have the luxury to work full-time on LTTng

mainlining in 2010

  • Work undertaken in collaboration with

– Ericsson, Nokia, Wind River, Freescale, Mentor

Graphics, Monta Vista, Sony, CELF

  • Plan

– Vertical integration of static instrumentation and

metadata

  • TRACE_EVENT()

– Horizontal integration of the LTTng tracer core

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April 15th, 2010 Mathieu Desnoyers 21

> LTTng core merge plan

  • Cleanup of the lttng tree
  • Extraction of the LTTng tracer core into

approximately 50 patches

– Create temporary branch lttng-staging

  • Send piecewise (5 patches at a time) on LKML for

review, with pointer to lttng-staging

– Merge incrementally into branch lttng-for-mainline

  • Git pull request when done with the whole branch
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April 15th, 2010 Mathieu Desnoyers 22

> Conclusion

  • Linux instrumentation has made good progress

in 2009

  • Requirements differ between kernel developers

and many Linux end-users

  • Need for a kernel tracer fulfilling these user

requirements

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April 15th, 2010 Mathieu Desnoyers 23

> Questions ?

?

– http://www.efficios.com

  • LTTng Information

– http://lttng.org – ltt-dev@lists.casi.polymtl.ca

  • Tracing Mini-Summit at LinuxCon 2010

– http://lttng.org/tracingsummit