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Message-ID: <530A9B67.1050403@intel.com> Date: Mon, 24 Feb 2014 09:07:51 +0800 From: "Yan, Zheng" <zheng.z.yan@...el.com> To: Stephane Eranian <eranian@...gle.com> CC: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...nel.org>, Arnaldo Carvalho de Melo <acme@...radead.org>, Andi Kleen <andi@...stfloor.org> Subject: Re: [PATCH v3 00/14] perf, x86: Haswell LBR call stack support On 02/24/2014 03:47 AM, Stephane Eranian wrote: > Could you add the Reviewed-by: on the patches I already > reviewed? So I focus on the changes you made and continue > testing on my HSW system. > Hi, I got your Reviewed-by for patch 1,5,6,8. Patch 6 was changed in this series. So only patch 1,6,8 were left (they all are simple change). I will add your Reviewed-by in next version. Regards Yan, Zheng > Thanks. > > On Tue, Feb 18, 2014 at 7:07 AM, Yan, Zheng <zheng.z.yan@...el.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 >> >> 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 >> >> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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