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Wed, 27 May 2020 18:40:33 +0000 From: Song Liu To: Masami Hiramatsu CC: Peter Zijlstra , linux-kernel , Kernel Team , Ingo Molnar , Steven Rostedt , "Arnaldo Carvalho de Melo" , Mark Rutland , Jiri Olsa , Namhyung Kim , Alexey Budankov Subject: Re: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c Thread-Topic: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c Thread-Index: AQHWM6ViVS5deg/n5kWgZSYX+yJPDqi65OeAgAACB4CAAIR9AIAA2eQA Date: Wed, 27 May 2020 18:40:33 +0000 Message-ID: References: <20200526212826.4097888-1-songliubraving@fb.com> <20200526213913.GG2483@worktop.programming.kicks-ass.net> <20200527144040.3f12026f31b20b2011fbbcee@kernel.org> In-Reply-To: <20200527144040.3f12026f31b20b2011fbbcee@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.80.23.2.2) authentication-results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=fb.com; 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Allow ftrace f= or >>>> them by removing $(CC_FLAGS_FTRACE) from Makefile. >>>=20 >>> Did you try using the ftrace event with perf with this on? >>=20 >> I have tried a few things, like=20 >>=20 >> perf stat -e probe:perf_read -I 1000 >> perf record -e probe:__x64_sys_perf_event_open -aR >>=20 >> They all work fine.=20 >=20 > Did you try using perf with function-tracer or function-graph tracer? > If you just want to trace those functions with kprobes, you can=20 > build your kernel with CONFIG_KPROBE_EVENTS_ON_NOTRACE=3Dy, which allows > you to probe perf_read etc. Thanks for the hint.=20 kprobe does work with CONFIG_KPROBE_EVENTS_ON_NOTRACE, but BPF trampoline doesn't work. If it is safe, removing $(CC_FLAGS_FTRACE) is preferable. Thanks, Song