Re: [PATCH bpf-next v8] selftests/bpf: trace_helpers.c: optimize kallsyms cache

From: Jiri Olsa <olsajiri@gmail.com>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: "Rong Tao" <rtoax@foxmail.com>,
	olsajiri@gmail.com, andrii@kernel.org, daniel@iogearbox.net,
	sdf@google.com, "Rong Tao" <rongtao@cestc.cn>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>, "Hao Luo" <haoluo@google.com>,
	"Mykola Lysenko" <mykolal@fb.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
	"Alexandre Torgue" <alexandre.torgue@foss.st.com>,
	"Ilya Leoshkevich" <iii@linux.ibm.com>,
	"Daniel Müller" <deso@posteo.net>,
	"Manu Bretelle" <chantr4@gmail.com>,
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	"Ross Zwisler" <zwisler@google.com>,
	"Eduard Zingerman" <eddyz87@gmail.com>,
	"open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)"
	<bpf@vger.kernel.org>, "open list" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH bpf-next v8] selftests/bpf: trace_helpers.c: optimize kallsyms cache
Date: Sun, 27 Aug 2023 11:39:02 +0200	[thread overview]
Message-ID: <ZOsZtjw3NAeMdWfv@krava> (raw)
In-Reply-To: <CALOAHbCXVNXk4WUCRGCDsezzTfieDcLT=Jt00m4UX4zdw=RtsQ@mail.gmail.com>

On Sun, Aug 27, 2023 at 10:48:44AM +0800, Yafang Shao wrote:
> On Sat, Aug 26, 2023 at 10:46 PM Rong Tao <rtoax@foxmail.com> wrote:
> >
> > From: Rong Tao <rongtao@cestc.cn>
> >
> > Static ksyms often have problems because the number of symbols exceeds the
> > MAX_SYMS limit. Like changing the MAX_SYMS from 300000 to 400000 in
> > commit e76a014334a6("selftests/bpf: Bump and validate MAX_SYMS") solves
> > the problem somewhat, but it's not the perfect way.
> >
> > This commit uses dynamic memory allocation, which completely solves the
> > problem caused by the limitation of the number of kallsyms.
> >
> > Acked-by: Stanislav Fomichev <sdf@google.com>
> > Signed-off-by: Rong Tao <rongtao@cestc.cn>
> > ---
> > v8: Resolves inter-thread contention for ksyms global variables.
> > v7: https://lore.kernel.org/lkml/tencent_BD6E19C00BF565CD5C36A9A0BD828CFA210A@qq.com/
> >     Fix __must_check macro.
> > v6: https://lore.kernel.org/lkml/tencent_4A09A36F883A06EA428A593497642AF8AF08@qq.com/
> >     Apply libbpf_ensure_mem()
> > v5: https://lore.kernel.org/lkml/tencent_0E9E1A1C0981678D5E7EA9E4BDBA8EE2200A@qq.com/
> >     Release the allocated memory once the load_kallsyms_refresh() upon error
> >     given it's dynamically allocated.
> > v4: https://lore.kernel.org/lkml/tencent_59C74613113F0C728524B2A82FE5540A5E09@qq.com/
> >     Make sure most cases we don't need the realloc() path to begin with,
> >     and check strdup() return value.
> > v3: https://lore.kernel.org/lkml/tencent_50B4B2622FE7546A5FF9464310650C008509@qq.com/
> >     Do not use structs and judge ksyms__add_symbol function return value.
> > v2: https://lore.kernel.org/lkml/tencent_B655EE5E5D463110D70CD2846AB3262EED09@qq.com/
> >     Do the usual len/capacity scheme here to amortize the cost of realloc, and
> >     don't free symbols.
> > v1: https://lore.kernel.org/lkml/tencent_AB461510B10CD484E0B2F62E3754165F2909@qq.com/
> > ---
> >  samples/bpf/Makefile                          |   4 +
> >  samples/bpf/offwaketime_user.c                |   7 +-
> >  samples/bpf/sampleip_user.c                   |   9 +-
> >  samples/bpf/spintest_user.c                   |   7 +-
> >  samples/bpf/task_fd_query_user.c              |  13 +-
> >  samples/bpf/trace_event_user.c                |   7 +-
> >  .../selftests/bpf/prog_tests/bpf_cookie.c     |   7 +-
> >  .../selftests/bpf/prog_tests/fill_link_info.c |   9 +-
> >  .../bpf/prog_tests/get_stack_raw_tp.c         |  10 +-
> >  .../bpf/prog_tests/kprobe_multi_test.c        |  13 +-
> >  .../prog_tests/kprobe_multi_testmod_test.c    |  13 +-
> >  tools/testing/selftests/bpf/trace_helpers.c   | 116 ++++++++++++------
> >  tools/testing/selftests/bpf/trace_helpers.h   |  10 +-
> >  13 files changed, 154 insertions(+), 71 deletions(-)
> 
> I think we'd better split it into two patches: one for samples/bpf/
> and another for tools/testing/selftests/bpf.
> 
> BTW, why can't we just load it once for all ?  IOW, load the kallsyms
> before we start each individual test, and free it after all tests
> finish.

there are bpf_testmod tests that unload module so we need fresh
symbols after that

jirka

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