| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <Z2OxIBW0t4kLBAFW@google.com>
Date: Wed, 18 Dec 2024 21:37:36 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org
Subject: Re: [RFC/PATCH] perf trace: Add --syscall-period option
On Tue, Dec 17, 2024 at 09:40:21PM -0800, Howard Chu wrote:
> Hello Namhyung,
>
> Thanks for the patch.
>
> On Wed, Dec 11, 2024 at 2:21 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > This option is to implement the event sampling for system calls.
> > The period is given in msec as it shows the time in msec.
> >
> > # perf trace -C 0 --syscall-period 100 sleep 1
> > ? ( ): fleetspeakd/1828559 ... [continued]: futex()) = -1 ETIMEDOUT (Connection timed out)
> > 0.050 (100.247 ms): gnome-shell/572531 recvmsg(fd: 10<socket:[3355761]>, msg: 0x7ffef8b39d20) = 40
> > 100.357 (100.149 ms): pipewire-pulse/572245 read(fd: 5<anon_inode:[eventfd]>, buf: 0x7ffc0b9dc8f0, count: 8) = 8
> > 200.553 (100.268 ms): NetworkManager/3424 epoll_wait(epfd: 19<anon_inode:[eventpoll]>, events: 0x5607b85bb880, maxevents: 6) = 0
> > 300.876 ( ): mon/4932 poll(ufds: 0x7fa392784df0, nfds: 1, timeout_msecs: 100) ...
> > 400.901 ( 0.025 ms): TaskCon~ller #/620145 futex(uaddr: 0x7f3fc596fa00, op: WAKE|PRIVATE_FLAG, val: 1) = 0
> > 300.876 (100.123 ms): mon/4932 ... [continued]: poll()) = 0 (Timeout)
> > 500.901 ( 0.012 ms): evdefer/2/2335122 futex(uaddr: 0x5640baac5198, op: WAKE|PRIVATE_FLAG, val: 1) = 0
> > 602.701 ( 0.017 ms): Compositor/1992200 futex(uaddr: 0x7f1a51dfdd40, op: WAKE|PRIVATE_FLAG, val: 1) = 0
> > 705.589 ( 0.017 ms): JS Watchdog/947933 futex(uaddr: 0x7f4cac1d4240, op: WAKE|PRIVATE_FLAG, val: 1) = 0
> > 812.667 ( 0.027 ms): fix/1985151 futex(uaddr: 0xc0008f7148, op: WAKE|PRIVATE_FLAG, val: 1) = 1
> > 912.807 ( 0.017 ms): Xorg/572315 setitimer(value: 0x7ffc375d6ba0) = 0
> >
> > The timestamp is kept in a per-cpu array and the allowed task is saved
> > in a hash map.
> >
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> > tools/perf/Documentation/perf-trace.txt | 6 ++
> > tools/perf/builtin-trace.c | 5 ++
> > .../bpf_skel/augmented_raw_syscalls.bpf.c | 67 ++++++++++++++++++-
> > 3 files changed, 76 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/perf/Documentation/perf-trace.txt b/tools/perf/Documentation/perf-trace.txt
> > index 6e0cc50bbc13fc7f..9f338a8c5357a67e 100644
> > --- a/tools/perf/Documentation/perf-trace.txt
> > +++ b/tools/perf/Documentation/perf-trace.txt
> > @@ -241,6 +241,12 @@ the thread executes on the designated CPUs. Default is to monitor all CPUs.
> > printing using the existing 'perf trace' syscall arg beautifiers to map integer
> > arguments to strings (pid to comm, syscall id to syscall name, etc).
> >
> > +--syscall-period::
> > + Trace a system call in the given period (in msec). This implements
> > + sampling for syscalls in order to reduce the monitoring overhead.
> > + For example, setting the sysall period to 100 (msec) means it will
> > + sample a syscall and next one after 100 msec.
> > +
> >
> > PAGEFAULTS
> > ----------
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index 3c46de1a8d79bfe6..789eb0ffd5f90b61 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -185,6 +185,7 @@ struct trace {
> > } stats;
> > unsigned int max_stack;
> > unsigned int min_stack;
> > + unsigned long sample_period_ms;
> > int raw_augmented_syscalls_args_size;
> > bool raw_augmented_syscalls;
> > bool fd_path_disabled;
> > @@ -5219,6 +5220,7 @@ int cmd_trace(int argc, const char **argv)
> > "start"),
> > OPT_BOOLEAN(0, "force-btf", &trace.force_btf, "Prefer btf_dump general pretty printer"
> > "to customized ones"),
> > + OPT_ULONG(0, "syscall-period", &trace.sample_period_ms, "syscall sampling period in ms"),
> > OPTS_EVSWITCH(&trace.evswitch),
> > OPT_END()
> > };
> > @@ -5326,6 +5328,9 @@ int cmd_trace(int argc, const char **argv)
> > bpf_program__set_autoattach(prog, /*autoattach=*/false);
> > }
> >
> > + if (trace.sample_period_ms)
> > + trace.skel->rodata->sample_period = trace.sample_period_ms * NSEC_PER_MSEC;
> > +
> > err = augmented_raw_syscalls_bpf__load(trace.skel);
> >
> > if (err < 0) {
> > diff --git a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > index 4a62ed593e84edf8..12272620dcd73700 100644
> > --- a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > @@ -113,6 +113,22 @@ struct pids_filtered {
> > __uint(max_entries, 64);
> > } pids_filtered SEC(".maps");
> >
> > +struct sample_timestamp {
> > + __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
> > + __type(key, int);
> > + __type(value, __u64);
> > + __uint(max_entries, 1);
> > +} sample_timestamp SEC(".maps");
> > +
> > +struct sample_filtered {
> > + __uint(type, BPF_MAP_TYPE_HASH);
> > + __type(key, pid_t);
> > + __type(value, bool);
> > + __uint(max_entries, MAX_CPUS);
> > +} sample_filtered SEC(".maps");
>
> Do you think MAX_CPUS provides enough entries? If there are MAX_CPUS
> syscalls that have entered but haven't exited, new syscalls cannot
> write to the map, which results in the new syscall's sys_exit not
> being collected. This can lead to trace logs like the following:
>
> 210.947 ( ): tmux: server/4399 poll(ufds: 0x579c819eac40,
> nfds: 51, timeout_msecs: 9)
>
> which doesn't have a duration, because perf trace doesn't know when it
> exits. For example, a poll system call can take a long time to exit,
> if there are MAX_CPUS number of polls, they will occupy all the space
> in the sample_filtered map.
>
> > + if (prev_ts) {
> > + if ((*prev_ts + sample_period) > timestamp)
> > + return false;
> > + *prev_ts = timestamp;
> > + } else {
> > + bpf_map_update_elem(&sample_timestamp, &idx, ×tamp, BPF_ANY);
> > + }
> > +
> > + bpf_map_update_elem(&sample_filtered, &pid, &ok, BPF_ANY);
>
> and during polling, when a new syscall enters, this
> bpf_map_update_elem() will return an error and fail to insert, and in
> sys_exit(), this:
>
> > + if (!bpf_map_lookup_elem(&sample_filtered, &pid))
> > + return false;
>
> returns false, and creates a sample with no duration.
>
> In order to eliminate samples with no duration, there should be no
> more than MAX_CPUS simultaneous syscalls, but I haven't yet created a
> scenario where there are MAX_CPUS polls at the same time. (such
> creation needs some tricks, because --syscall-period=1 allows maximum
> <number-of-cpus> number of syscalls every millisecond)
>
> That said, I agree that MAX_CPUS (4096) is generally sufficient for
> the sample_filtered map in most situations.
Right, usually the number of CPUs is far less than that, but I remember
there's a system with more than 2K CPUs. I can add a command line
option to control the number of entries or change the default using the
actual number of CPUs in the system.
>
> Aside from this edge case, this patch looks good to me, I tested it with:
>
> perf trace --syscall-period=500
>
> 544.863 ( 0.008 ms): sshd/869528 rt_sigprocmask(how: UNBLOCK, nset:
> 0x7fffef5f71f0, oset: 0x7fffef5f7270, sigsetsize: 8) = 0
> 545.034 ( 0.007 ms): tmux: server/4399 ioctl(fd: 54</dev/ptmx>,
> cmd: FIONREAD, arg: 0x7ffe020ec758) = 0
> 593.054 (100.214 ms): gnome-shell/2419 poll(ufds: 0x6236d31eb850,
> nfds: 15, timeout_msecs: 100) = 0 (Timeout)
> 1073.251 ( 0.059 ms): gmain/38955 inotify_add_watch(fd:
> 4<anon_inode:inotify>, pathname:
> "/var/lib/fwupd/metadata/lvfs-testing", mask: 16789454) = -1 ENOENT
> (No such file or directory)
> 1073.641 ( 0.014 ms): tmux: server/4399 ioctl(fd: 54</dev/ptmx>,
> cmd: FIONREAD, arg: 0x7ffe020ec758) = 0
> 1074.588 ( 0.013 ms): sshd/869528 rt_sigprocmask(how: UNBLOCK, nset:
> 0x7fffef5f71f0, oset: 0x7fffef5f7270, sigsetsize: 8) = 0
> 1094.651 (100.370 ms): gnome-shell/2419 poll(ufds: 0x6236d31eb850,
> nfds: 15, timeout_msecs: 100) = 0 (Timeout)
> 1596.817 (100.363 ms): gnome-shell/2419 poll(ufds: 0x6236d31eb850,
> nfds: 15, timeout_msecs: 100)
>
> The timestamp makes sense for the 500 ms period.
Thanks for the review and test!
Namhyung
Powered by blists - more mailing lists