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Commit c5dfd78e authored by Arnaldo Carvalho de Melo's avatar Arnaldo Carvalho de Melo
Browse files

perf core: Allow setting up max frame stack depth via sysctl 



The default remains 127, which is good for most cases, and not even hit
most of the time, but then for some cases, as reported by Brendan, 1024+
deep frames are appearing on the radar for things like groovy, ruby.

And in some workloads putting a _lower_ cap on this may make sense. One
that is per event still needs to be put in place tho.

The new file is:

  # cat /proc/sys/kernel/perf_event_max_stack
  127

Chaging it:

  # echo 256 > /proc/sys/kernel/perf_event_max_stack
  # cat /proc/sys/kernel/perf_event_max_stack
  256

But as soon as there is some event using callchains we get:

  # echo 512 > /proc/sys/kernel/perf_event_max_stack
  -bash: echo: write error: Device or resource busy
  #

Because we only allocate the callchain percpu data structures when there
is a user, which allows for changing the max easily, its just a matter
of having no callchain users at that point.

Reported-and-Tested-by: default avatarBrendan Gregg <brendan.d.gregg@gmail.com>
Reviewed-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDavid Ahern <dsahern@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/20160426002928.GB16708@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent c2a218c6

Documentation/sysctl/kernel.txt

+14 −0
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ show up in /proc/sys/kernel: 
- panic_on_warn

- perf_cpu_time_max_percent

- perf_event_paranoid

- perf_event_max_stack

- pid_max

- powersave-nap               [ PPC only ]

- printk
@@ -654,6 +655,19 @@ users (without CAP_SYS_ADMIN). The default value is 1. 


==============================================================



perf_event_max_stack:



Controls maximum number of stack frames to copy for (attr.sample_type &

PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using

'perf record -g' or 'perf trace --call-graph fp'.



This can only be done when no events are in use that have callchains

enabled, otherwise writing to this file will return -EBUSY.



The default value is 127.



==============================================================



pid_max:



PID allocation wrap value.  When the kernel's next PID value

arch/arm/kernel/perf_callchain.c

+1 −1
Original line number Diff line number Diff line
@@ -75,7 +75,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) 


	tail = (struct frame_tail __user *)regs->ARM_fp - 1;



	while ((entry->nr < PERF_MAX_STACK_DEPTH) &&

	while ((entry->nr < sysctl_perf_event_max_stack) &&

	       tail && !((unsigned long)tail & 0x3))

		tail = user_backtrace(tail, entry);

}

arch/arm64/kernel/perf_callchain.c

+2 −2
Original line number Diff line number Diff line
@@ -122,7 +122,7 @@ void perf_callchain_user(struct perf_callchain_entry *entry, 


		tail = (struct frame_tail __user *)regs->regs[29];



		while (entry->nr < PERF_MAX_STACK_DEPTH &&

		while (entry->nr < sysctl_perf_event_max_stack &&

		       tail && !((unsigned long)tail & 0xf))

			tail = user_backtrace(tail, entry);

	} else {
@@ -132,7 +132,7 @@ void perf_callchain_user(struct perf_callchain_entry *entry, 


		tail = (struct compat_frame_tail __user *)regs->compat_fp - 1;



		while ((entry->nr < PERF_MAX_STACK_DEPTH) &&

		while ((entry->nr < sysctl_perf_event_max_stack) &&

			tail && !((unsigned long)tail & 0x3))

			tail = compat_user_backtrace(tail, entry);

#endif

arch/metag/kernel/perf_callchain.c

+1 −1
Original line number Diff line number Diff line
@@ -65,7 +65,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) 


	--frame;



	while ((entry->nr < PERF_MAX_STACK_DEPTH) && frame)

	while ((entry->nr < sysctl_perf_event_max_stack) && frame)

		frame = user_backtrace(frame, entry);

}

arch/mips/kernel/perf_event.c

+2 −2
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ static void save_raw_perf_callchain(struct perf_callchain_entry *entry, 
		addr = *sp++;

		if (__kernel_text_address(addr)) {

			perf_callchain_store(entry, addr);

			if (entry->nr >= PERF_MAX_STACK_DEPTH)

			if (entry->nr >= sysctl_perf_event_max_stack)

				break;

		}

	}
@@ -59,7 +59,7 @@ void perf_callchain_kernel(struct perf_callchain_entry *entry, 
	}

	do {

		perf_callchain_store(entry, pc);

		if (entry->nr >= PERF_MAX_STACK_DEPTH)

		if (entry->nr >= sysctl_perf_event_max_stack)

			break;

		pc = unwind_stack(current, &sp, pc, &ra);

	} while (pc);