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
>>