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Date: Fri, 16 Feb 2024 14:37:38 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] perf trace: Disable syscall augmentation with record
Message-ID: <Zc-dYrNMt3Wsinax@x1>
References: <20240216172357.65037-1-irogers@google.com>
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In-Reply-To: <20240216172357.65037-1-irogers@google.com>

On Fri, Feb 16, 2024 at 09:23:57AM -0800, Ian Rogers wrote:
> Syscall augmentation is causing samples not to be written to the
> perf.data file with "perf trace record". Disabling augmentation is
> sub-optimal, but it beats having a totally broken perf trace record.

Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

'perf trace record' needs to be more tested, we need to have a shell
'perf test' for it, maybe Michael has something on his test suite?

Testing your patch:

root@number:~# perf trace record ls
anaconda-ks.cfg  bin  perf.all-number-20231219-104854.tar.bz2  perfconfig.off  perf.data  perf.data.baseline  perf.data.old
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.050 MB perf.data (170 samples) ]
root@number:~# perf evlist -v
raw_syscalls:sys_enter: type: 2 (PERF_TYPE_TRACEPOINT), size: 136, config: 0x168 (raw_syscalls:sys_enter), { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|PERIOD|RAW|IDENTIFIER, read_format: ID|LOST, disabled: 1, inherit: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
raw_syscalls:sys_exit: type: 2 (PERF_TYPE_TRACEPOINT), size: 136, config: 0x167 (raw_syscalls:sys_exit), { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|PERIOD|RAW|IDENTIFIER, read_format: ID|LOST, disabled: 1, inherit: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
dummy:u: type: 1 (PERF_TYPE_SOFTWARE), size: 136, config: 0x9 (PERF_COUNT_SW_DUMMY), { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|IDENTIFIER, read_format: ID|LOST, inherit: 1, exclude_kernel: 1, exclude_hv: 1, mmap: 1, comm: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
# Tip: use 'perf evlist --trace-fields' to show fields for tracepoint events
root@number:~# perf script | head -5
              ls  145954 [021] 64113.916047:  raw_syscalls:sys_exit: NR 59 = 0
              ls  145954 [021] 64113.916065: raw_syscalls:sys_enter: NR 12 (0, 528, 0, 0, 0, 27)
              ls  145954 [021] 64113.916065:  raw_syscalls:sys_exit: NR 12 = 94098335809536
              ls  145954 [021] 64113.916077: raw_syscalls:sys_enter: NR 158 (3001, 7fff9bc13790, 7f4bd6f4b4c0, 1, 3, 800)
              ls  145954 [021] 64113.916078:  raw_syscalls:sys_exit: NR 158 = -22
root@number:~# perf trace -i perf.data |& head 
         ? (         ): ls/145954  ... [continued]: execve())                                           = 0
     0.018 ( 0.000 ms): ls/145954 brk()                                                                 = 0x5594f9e14000
     0.030 ( 0.000 ms): ls/145954 arch_prctl(option: 0x3001, arg2: 0x7fff9bc13790)                      = -1 EINVAL (Invalid argument)
     0.045 ( 0.002 ms): ls/145954 access(filename: 0xd6f5b2c0, mode: R)                                 = -1 ENOENT (No such file or directory)
     0.050 ( 0.003 ms): ls/145954 openat(dfd: CWD, filename: 0xd6f5a144, flags: RDONLY|CLOEXEC)         = 3
     0.053 ( 0.001 ms): ls/145954 newfstatat(dfd: 3, filename: 0xd6f5ace8, statbuf: 0x7fff9bc129a0, flag: 4096) = 0
     0.055 ( 0.004 ms): ls/145954 mmap(len: 78087, prot: READ, flags: PRIVATE, fd: 3)                   = 0x7f4bd6f1c000
     0.059 ( 0.000 ms): ls/145954 close(fd: 3)                                                          = 0
     0.066 ( 0.003 ms): ls/145954 openat(dfd: CWD, filename: 0xd6f65fa0, flags: RDONLY|CLOEXEC)         = 3
     0.068 ( 0.001 ms): ls/145954 read(fd: 3, buf: 0x7fff9bc12b08, count: 832)                          = 832
root@number:~#

root@number:~# perf trace -v record ls
Syscall augmentation fails with record, disabling augmentationUsing CPUID GenuineIntel-6-B7-1
DEBUGINFOD_URLS=
nr_cblocks: 0
affinity: SYS
mmap flush: 1
comp level: 0
mmap size 4198400B
Control descriptor is not initialized
mmap size 528384B
anaconda-ks.cfg  bin  perf.all-number-20231219-104854.tar.bz2  perfconfig.off  perf.data  perf.data.baseline  perf.data.old
[ perf record: Woken up 1 times to write data ]
failed to write feature CPU_PMU_CAPS
[ perf record: Captured and wrote 0.050 MB perf.data (170 samples) ]
root@number:~#

There is a missing newline and we can avoid repeating a term, and I also
added some extra explanation about "augmentation":

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 192721261098832e..3f77dd3eb70dc37a 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -4865,7 +4865,7 @@ int cmd_trace(int argc, const char **argv)
 		goto skip_augmentation;
 
 	if ((argc >= 1) && (strcmp(argv[0], "record") == 0)) {
-		pr_debug("Syscall augmentation fails with record, disabling augmentation");
+		pr_debug("Syscall augmentation (reading pointer args using BPF) fails with record, disabling it.\n");
 		goto skip_augmentation;
 	}
 
I'll see if I come up with the test and a fix that allows augmentation
to work with 'perf trace record'.

- Arnaldo

 
> Closes: https://lore.kernel.org/lkml/CAP-5=fV9Gd1Teak+EOcUSxe13KqSyfZyPNagK97GbLiOQRgGaw@mail.gmail.com/
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/builtin-trace.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 109b8e64fe69..192721261098 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -4864,6 +4864,11 @@ int cmd_trace(int argc, const char **argv)
>  	if (!trace.trace_syscalls)
>  		goto skip_augmentation;
>  
> +	if ((argc >= 1) && (strcmp(argv[0], "record") == 0)) {
> +		pr_debug("Syscall augmentation fails with record, disabling augmentation");
> +		goto skip_augmentation;
> +	}
> +
>  	trace.skel = augmented_raw_syscalls_bpf__open();
>  	if (!trace.skel) {
>  		pr_debug("Failed to open augmented syscalls BPF skeleton");
> -- 
> 2.44.0.rc0.258.g7320e95886-goog
>