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- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Liang, Kan"
| | | Date | Fri, 5 Sep 2014 17:20:56 +0200 | Subject | Re: [PATCH v5 00/16] perf, x86: Haswell LBR call stack support | From | Stephane Eranian <> |
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On Fri, Sep 5, 2014 at 4:25 PM, Liang, Kan <kan.liang@intel.com> wrote: > Hi Peter and all, > > Did you get a chance to review these patches? > Zheng is away. Should I re-send the patches? > Please resubmit rebased to tip.git and I'll take another look.
> Thanks, > Kan > >> >> 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. >> >> 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 >> >> Changes since v1 >> - 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 >> >> Changes since v2 >> - don't use xchg to switch PMU specific data >> - remove nr_branch_stack from struct perf_event_context >> - simplify the save/restore LBR stack logical >> - remove unnecessary 'has_branch_stack -> needs_branch_stack' >> conversion >> - more description in change logs >> >> Changes since v3 >> - remove sysfs attribute file that disable this feature >> >> Changes since v4 >> - re-organize code that save/resotre LBR stack >> - allocate pmu specific data when it's needed >> - update code comments >> >> These patches are also available at: >> >> These patches are also available at: >> https://github.com/ukernel/linux.git perf-lbr-callstack >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the >> body of a message to majordomo@vger.kernel.org More majordomo info at >> http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/
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