Messages in this thread | | | Date | Wed, 25 Oct 2023 21:35:00 +0300 | Subject | Re: [PATCH v3 12/50] perf record: Lazy load kernel symbols | From | Adrian Hunter <> |
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On 25/10/23 21:25, Namhyung Kim wrote: > Hi Ian, > > On Tue, Oct 24, 2023 at 3:24 PM Ian Rogers <irogers@google.com> wrote: >> >> Commit 5b7ba82a7591 ("perf symbols: Load kernel maps before using") >> changed it so that loading a kernel dso would cause the symbols for >> the dso to be eagerly loaded. For perf record this is overhead as the >> symbols won't be used. Add a symbol_conf to control the behavior and >> disable it for perf record and perf inject. > > I'm curious if it can simply move to lazy loading unconditionally. > In most cases, the code calls machine__resolve() which calls > thread__find_map() and map__find_symbol() to load symbols. > > So I think it's unnecessary to do it in the thread__find_map(). > If it needs a symbol, it should call map__find_symbol() first > and it'll load the symbol table. > > Adrian, what's special in inject or Intel-PT on this?
Was a long time ago. Apart from what the commit says below, I think there might also be other changes to the kernel maps that happen at loading, but I would have to have a look.
commit 5b7ba82a75915e739709d0ace4bb559cb280db09 Author: Adrian Hunter <adrian.hunter@intel.com> Date: Wed Aug 7 14:38:46 2013 +0300
perf symbols: Load kernel maps before using
In order to use kernel maps to read object code, those maps must be adjusted to map to the dso file offset. Because lazy-initialization is used, that is not done until symbols are loaded. However the maps are first used by thread__find_addr_map() before symbols are loaded. So this patch changes thread__find_addr() to "load" kernel maps before using them.
> > Thanks, > Namhyung > > >> >> Signed-off-by: Ian Rogers <irogers@google.com> >> --- >> tools/perf/builtin-inject.c | 6 ++++++ >> tools/perf/builtin-record.c | 2 ++ >> tools/perf/util/event.c | 4 ++-- >> tools/perf/util/symbol_conf.h | 3 ++- >> 4 files changed, 12 insertions(+), 3 deletions(-) >> >> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c >> index c8cf2fdd9cff..eb3ef5c24b66 100644 >> --- a/tools/perf/builtin-inject.c >> +++ b/tools/perf/builtin-inject.c >> @@ -2265,6 +2265,12 @@ int cmd_inject(int argc, const char **argv) >> "perf inject [<options>]", >> NULL >> }; >> + >> + if (!inject.itrace_synth_opts.set) { >> + /* Disable eager loading of kernel symbols that adds overhead to perf inject. */ >> + symbol_conf.lazy_load_kernel_maps = true; >> + } >> + >> #ifndef HAVE_JITDUMP >> set_option_nobuild(options, 'j', "jit", "NO_LIBELF=1", true); >> #endif >> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c >> index dcf288a4fb9a..8ec818568662 100644 >> --- a/tools/perf/builtin-record.c >> +++ b/tools/perf/builtin-record.c >> @@ -3989,6 +3989,8 @@ int cmd_record(int argc, const char **argv) >> # undef set_nobuild >> #endif >> >> + /* Disable eager loading of kernel symbols that adds overhead to perf record. */ >> + symbol_conf.lazy_load_kernel_maps = true; >> rec->opts.affinity = PERF_AFFINITY_SYS; >> >> rec->evlist = evlist__new(); >> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c >> index 923c0fb15122..68f45e9e63b6 100644 >> --- a/tools/perf/util/event.c >> +++ b/tools/perf/util/event.c >> @@ -617,13 +617,13 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr, >> if (cpumode == PERF_RECORD_MISC_KERNEL && perf_host) { >> al->level = 'k'; >> maps = machine__kernel_maps(machine); >> - load_map = true; >> + load_map = !symbol_conf.lazy_load_kernel_maps; >> } else if (cpumode == PERF_RECORD_MISC_USER && perf_host) { >> al->level = '.'; >> } else if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL && perf_guest) { >> al->level = 'g'; >> maps = machine__kernel_maps(machine); >> - load_map = true; >> + load_map = !symbol_conf.lazy_load_kernel_maps; >> } else if (cpumode == PERF_RECORD_MISC_GUEST_USER && perf_guest) { >> al->level = 'u'; >> } else { >> diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h >> index 0b589570d1d0..2b2fb9e224b0 100644 >> --- a/tools/perf/util/symbol_conf.h >> +++ b/tools/perf/util/symbol_conf.h >> @@ -42,7 +42,8 @@ struct symbol_conf { >> inline_name, >> disable_add2line_warn, >> buildid_mmap2, >> - guest_code; >> + guest_code, >> + lazy_load_kernel_maps; >> const char *vmlinux_name, >> *kallsyms_name, >> *source_prefix, >> -- >> 2.42.0.758.gaed0368e0e-goog >>
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