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    SubjectRe: [PATCH 00/14] perf, x86: Haswell LBR call stack support
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    Hi,

    Is there a git tree from which I could could pull those 14 patches from?

    On Fri, Jan 3, 2014 at 6:47 AM, Yan, Zheng <zheng.z.yan@intel.com> wrote:
    > For many profiling tasks we need the callgraph. For example we often
    > need to see the caller of a lock or the caller of a memcpy or other
    > library function to actually tune the program. Frame pointer unwinding
    > is efficient and works well. But frame pointers are off by default on
    > 64bit code (and on modern 32bit gccs), so there are many binaries around
    > that do not use frame pointers. Profiling unchanged production code is
    > very useful in practice. On some CPUs frame pointer also has a high
    > cost. Dwarf2 unwinding also does not always work and is extremely slow
    > (upto 20% overhead).
    >
    > Haswell has a new feature that utilizes the existing Last Branch Record
    > facility to record call chains. When the feature is enabled, function
    > call will be collected as normal, but as return instructions are
    > executed the last captured branch record is popped from the on-chip LBR
    > registers. The LBR call stack facility provides an alternative to get
    > callgraph. It has some limitations too, but should work in most cases
    > and is significantly faster than dwarf. Frame pointer unwinding is still
    > the best default, but LBR call stack is a good alternative when nothing
    > else works.
    >
    > This patch series adds LBR call stack support. User can enabled/disable
    > this through an sysfs attribute file in the CPU PMU directory:
    > echo 1 > /sys/bus/event_source/devices/cpu/lbr_callstack
    >
    > When profiling bc(1) on Fedora 19:
    > echo 'scale=2000; 4*a(1)' > cmd; perf record -g fp bc -l < cmd
    >
    > If this feature is enabled, perf report output looks like:
    > 50.36% bc bc [.] bc_divide
    > |
    > --- bc_divide
    > execute
    > run_code
    > yyparse
    > main
    > __libc_start_main
    > _start
    >
    > 33.66% bc bc [.] _one_mult
    > |
    > --- _one_mult
    > bc_divide
    > execute
    > run_code
    > yyparse
    > main
    > __libc_start_main
    > _start
    >
    > 7.62% bc bc [.] _bc_do_add
    > |
    > --- _bc_do_add
    > |
    > |--99.89%-- 0x2000186a8
    > --0.11%-- [...]
    >
    > 6.83% bc bc [.] _bc_do_sub
    > |
    > --- _bc_do_sub
    > |
    > |--99.94%-- bc_add
    > | execute
    > | run_code
    > | yyparse
    > | main
    > | __libc_start_main
    > | _start
    > --0.06%-- [...]
    >
    > 0.46% bc libc-2.17.so [.] __memset_sse2
    > |
    > --- __memset_sse2
    > |
    > |--54.13%-- bc_new_num
    > | |
    > | |--51.00%-- bc_divide
    > | | execute
    > | | run_code
    > | | yyparse
    > | | main
    > | | __libc_start_main
    > | | _start
    > | |
    > | |--30.46%-- _bc_do_sub
    > | | bc_add
    > | | execute
    > | | run_code
    > | | yyparse
    > | | main
    > | | __libc_start_main
    > | | _start
    > | |
    > | --18.55%-- _bc_do_add
    > | bc_add
    > | execute
    > | run_code
    > | yyparse
    > | main
    > | __libc_start_main
    > | _start
    > |
    > --45.87%-- bc_divide
    > execute
    > run_code
    > yyparse
    > main
    > __libc_start_main
    > _start
    >
    > If this feature is disabled, perf report output looks like:
    > 50.49% bc bc [.] bc_divide
    > |
    > --- bc_divide
    >
    > 33.57% bc bc [.] _one_mult
    > |
    > --- _one_mult
    >
    > 7.61% bc bc [.] _bc_do_add
    > |
    > --- _bc_do_add
    > 0x2000186a8
    >
    > 6.88% bc bc [.] _bc_do_sub
    > |
    > --- _bc_do_sub
    >
    > 0.42% bc libc-2.17.so [.] __memcpy_ssse3_back
    > |
    > --- __memcpy_ssse3_back
    >
    > The LBR call stack has following known limitations
    > - Zero length calls are not filtered out by hardware
    > - Exception handing such as setjmp/longjmp will have calls/returns not
    > match
    > - Pushing different return address onto the stack will have calls/returns
    > not match
    > - If callstack is deeper than the LBR, only the last entries are captured
    >
    > Change since previous version
    > - split change into more patches
    > - introduce context switch callback and use it to flush LBR
    > - use the context switch callback to save/restore LBR
    > - dynamic allocate memory area for storing LBR stack, always switch the
    > memory area during context switch
    > - disable this feature by default
    > - more description in change logs
    >


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