lkml.org 
[lkml]   [2014]   [Jan]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 00/14] perf, x86: Haswell LBR call stack support
From
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
>


\
 
 \ /
  Last update: 2014-01-21 15:01    [W:0.239 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site