Older blog entries for mjw (starting at number 222)

commit 654443e20dfc0617231f28a07c96a979ee1a0239
Merge: 2c01e7b 9cba26e
Author: Linus Torvalds
Date:   Thu May 24 11:39:34 2012 -0700

    Merge branch 'perf-uprobes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

    Pull user-space probe instrumentation from Ingo Molnar:
     "The uprobes code originates from SystemTap and has been used for years
      in Fedora and RHEL kernels.  This version is much rewritten, reviews
      from PeterZ, Oleg and myself shaped the end result.

      This tree includes uprobes support in 'perf probe' - but SystemTap
      (and other tools) can take advantage of user probe points as well.

      Sample usage of uprobes via perf, for example to profile malloc()
      calls without modifying user-space binaries.

      First boot a new kernel with CONFIG_UPROBE_EVENT=y enabled.

      If you don't know which function you want to probe you can pick one
      from 'perf top' or can get a list all functions that can be probed
      within libc (binaries can be specified as well):

    	$ perf probe -F -x /lib/libc.so.6

      To probe libc's malloc():

    	$ perf probe -x /lib64/libc.so.6 malloc
    	Added new event:
    	probe_libc:malloc    (on 0x7eac0)

      You can now use it in all perf tools, such as:

    	perf record -e probe_libc:malloc -aR sleep 1

      Make use of it to create a call graph (as the flat profile is going to
      look very boring):

    	$ perf record -e probe_libc:malloc -gR make
    	[ perf record: Woken up 173 times to write data ]
    	[ perf record: Captured and wrote 44.190 MB perf.data (~1930712

    	$ perf report | less

    	  32.03%            git  libc-2.15.so   [.] malloc
    	                    |
    	                    --- malloc

    	  29.49%            cc1  libc-2.15.so   [.] malloc
    	                    |
    	                    --- malloc
    	                       |
    	                       |--0.95%-- 0x208eb1000000000
    	                       |
    	                       |--0.63%-- htab_traverse_noresize

    	  11.04%             as  libc-2.15.so   [.] malloc
    	                     |
    	                     --- malloc
    	                        |

    	   7.15%             ld  libc-2.15.so   [.] malloc
    	                     |
    	                     --- malloc
    	                        |

    	   5.07%             sh  libc-2.15.so   [.] malloc
    	                     |
    	                     --- malloc
    	                        |
    	   4.99%  python-config  libc-2.15.so   [.] malloc
    	          |
    	          --- malloc
    	             |
    	   4.54%           make  libc-2.15.so   [.] malloc
    	                   |
    	                   --- malloc
    	                      |
    	                      |--7.34%-- glob
    	                      |          |
    	                      |          |--93.18%-- 0x41588f
    	                      |          |
    	                      |           --6.82%-- glob
    	                      |                     0x41588f

    	   ...

      Or:

    	$ perf report -g flat | less

    	# Overhead        Command  Shared Object      Symbol
    	# ........  .............  .............  ..........
    	#
    	  32.03%            git  libc-2.15.so   [.] malloc
    	          27.19%
    	              malloc

    	  29.49%            cc1  libc-2.15.so   [.] malloc
    	          24.77%
    	              malloc

    	  11.04%             as  libc-2.15.so   [.] malloc
    	          11.02%
    	              malloc

    	   7.15%             ld  libc-2.15.so   [.] malloc
    	           6.57%
    	              malloc

    	 ...

      The core uprobes design is fairly straightforward: uprobes probe
      points register themselves at (inode:offset) addresses of
      libraries/binaries, after which all existing (or new) vmas that map
      that address will have a software breakpoint injected at that address.
      vmas are COW-ed to preserve original content.  The probe points are
      kept in an rbtree.

      If user-space executes the probed inode:offset instruction address
      then an event is generated which can be recovered from the regular
      perf event channels and mmap-ed ring-buffer.

      Multiple probes at the same address are supported, they create a
      dynamic callback list of event consumers.

      The basic model is further complicated by the XOL speedup: the
      original instruction that is probed is copied (in an architecture
      specific fashion) and executed out of line when the probe triggers.
      The XOL area is a single vma per process, with a fixed number of
      entries (which limits probe execution parallelism).

      The API: uprobes are installed/removed via
      /sys/kernel/debug/tracing/uprobe_events, the API is integrated to
      align with the kprobes interface as much as possible, but is separate
      to it.

      Injecting a probe point is privileged operation, which can be relaxed
      by setting perf_paranoid to -1.

      You can use multiple probes as well and mix them with kprobes and
      regular PMU events or tracepoints, when instrumenting a task."

    Fix up trivial conflicts in mm/memory.c due to previous cleanup of
    unmap_single_vma().

    * 'perf-uprobes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
      perf probe: Detect probe target when m/x options are absent
      perf probe: Provide perf interface for uprobes
      tracing: Fix kconfig warning due to a typo
      tracing: Provide trace events interface for uprobes
      tracing: Extract out common code for kprobes/uprobes trace events
      tracing: Modify is_delete, is_return from int to bool
      uprobes/core: Decrement uprobe count before the pages are unmapped
      uprobes/core: Make background page replacement logic account for rss_stat counters
      uprobes/core: Optimize probe hits with the help of a counter
      uprobes/core: Allocate XOL slots for uprobes use
      uprobes/core: Handle breakpoint and singlestep exceptions
      uprobes/core: Rename bkpt to swbp
      uprobes/core: Make order of function parameters consistent across functions
      uprobes/core: Make macro names consistent
      uprobes: Update copyright notices
      uprobes/core: Move insn to arch specific structure
      uprobes/core: Remove uprobe_opcode_sz
      uprobes/core: Make instruction tables volatile
      uprobes: Move to kernel/events/
      uprobes/core: Clean up, refactor and improve the code
      ...