Hi, Lassi:
The unwind cost is a major problem that bothers me now. I explain in detail
about my system.
I write a profiling service in a cloud system. This system will sampling
the all CPUs in a machine, and the cloud system will have thousands machines.
The sampling frequency is 10 Hz. All OS are rhel5u7, the x86_64 version. The
libunwind is the latest version (I got it use git).
All programs are wrote by C/C++, compiler is GCC/G++, the version is 4.1.2.
I got the sampling information like perf. The stack, registers are saved in
kernel, then use the external walking to unwind the stack. The APIs I used is
like:
unw_create_addr_space()
unw_init_remote()
static unw_accessors_t accessors = {
.find_proc_info = find_proc_info,
.put_unwind_info = put_unwind_info,
.get_dyn_info_list_addr = get_dyn_info_list_addr,
.access_mem = access_mem,
.access_reg = access_reg,
.access_fpreg = access_fpreg,
.resume = resume,
.get_proc_name = get_proc_name,
};
It must be a slow method.
I read the email:
https://lists.nongnu.org/archive/html/libunwind-devel/2011-03/msg00042.html
It look like a faster method. Does it use different APIs?
Regards Chenggang
3x
At 2014-11-22 21:16:11, "Lassi Tuura" <[email protected]> wrote:
That doesn't sound normal to me, but how exactly are you doing the walking?
What operating system are you using, is it 32- or 64-bit, which library
version, how did you build it, are you using external (ptrace) or in-process
(UNW_LOCAL_ONLY) walking, what exact API are you calling to walk, what language
and compiler did you use for your program, etc.?
Here are some reference numbers from another profiling tool (igprof) using
libunwind a few years back:
https://lists.nongnu.org/archive/html/libunwind-devel/2011-03/msg00042.html
https://lists.nongnu.org/archive/html/libunwind-devel/2011-03/msg00064.html
https://lists.nongnu.org/archive/html/libunwind-devel/2011-03/msg00079.html
The time in clock cycles to walk on average 30-ish stack frames, for very
frequent walks (3M/sec) was in the ballpark of 2500, and 70000 for less
frequent setitimer interrupts at 200/sec (~5 ms interrupt).
On Sat, Nov 22, 2014 at 10:05 AM, Chenggang <[email protected]> wrote:
Hi:
I am a user of libunwind. I am developing a profiling system, "Bianque".
I use libunwind to unwind the stack on the target machine. But the time
cost is too expensive.
While the layers of call chain is 130 and the stack size is 1MB, we need
3.8 milliseconds to unwind it.
My CPU is Xeon(R) CPU E5-2430 0 @ 2.20GHz.
Is this cost normal?
Regards
Chenggang
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