CODEWITHSUNDEEP
linuxlinux-kernelperf
John Zwinck
John Zwinck

Reputation: 249153

perf: why don't I have "syscall" counters?

There are apparently some counters in Linux perf like syscall:sys_enter_select, but on my system perf list does not show any of them

Evidence that other people do have these counters is here: http://www.brendangregg.com/blog/2014-07-03/perf-counting.html

If I run perf top -e 'syscalls:sys_enter_*' it says:

Can't open event dir: Permission denied
invalid or unsupported event: 'syscalls:sys_enter_*'

Other event types (the ones in perf list) work fine.

What do I need to do to access syscall counters in perf? I'm using Linux kernel and perf version 3.10 on x86_64.

Upvotes: 5

Views: 3249

Answers (3)

Peter Cordes
Peter Cordes

Reputation: 364180

You must have an old version of perf to go with your crusty old 3.10 kernel.

On a modern system (x86-64 Arch Linux with Linux 4.15.8-1-ARCH, and a matching version of perf), perf answers this question for you:

$ perf stat -e 'syscalls:sys_enter_*stat*' ls -l
event syntax error: 'syscalls:sys_enter_*stat*'
                     \___ can't access trace events

Error:  No permissions to read /sys/kernel/debug/tracing/events/syscalls/sys_enter_*stat*
Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'

Run 'perf list' for a list of valid events
...


$ ll /sys/kernel/debug/ -d
drwx------ 33 root root 0 Mar 14 00:02 /sys/kernel/debug/

Interesting that you could make it world-readable, similar to how you can put kernel.perf_event_paranoid = 0 and kernel.yama.ptrace_scope = 0 in /etc/sysctl.d/99-local.conf for convenient debugging / tracing / profiling on a single-user desktop without using root all the time.

Upvotes: 3

John Zwinck
John Zwinck

Reputation: 249153

Some perf counters, including all the syscall ones, are only available to the root user. sudo perf list will show all the counters, including syscall ones assuming the kernel is built with CONFIG_HAVE_SYSCALL_TRACEPOINTS (see Grisha Levit's answer regarding that).

So, to make perf top -e 'syscalls:sys_enter_*' work, run it under sudo--even if you do not need sudo for other counters like cycles.

Upvotes: 7

Grisha Levit
Grisha Levit

Reputation: 8617

These will be missing if the kernel was not built with CONFIG_HAVE_SYSCALL_TRACEPOINTS.

You can check like so:

# grep TRACEPOINTS "/boot/config-$(uname -r)"
CONFIG_TRACEPOINTS=y
CONFIG_HAVE_SYSCALL_TRACEPOINTS=y

Upvotes: 2

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