Messages in this thread | | | Date | Fri, 11 Aug 2017 11:01:27 +0100 | From | Mark Rutland <> | Subject | Re: perf: multiple mmap of fd behavior on x86/ARM |
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On Thu, Aug 10, 2017 at 02:48:52PM -0400, Vince Weaver wrote: > > So I was working on my perf_event_tests on ARM/ARM64 (the end goal was to > get ARM64 rdpmc support working, but apparently those patches never made > it upstream?)
IIUC by 'rdpmc' you mean direct userspace counter access?
Patches for that never made it upstream. Last I saw, there were no patches in a suitable state for review.
There are also difficulties (e.g. big.LITTLE systems where the number of counters can differ across CPUs) which have yet to be solved.
> anyway one test was failing due to an x86/arm difference, which is > possibly only tangentially perf related. > > On x86 you can mmap() a perf_event_open() file descriptor multiple times > and it works. > > On ARM/ARM64 you can only mmap() it once, any other attempts fail.
Interesting. Which platform(s) are you testing on, with which kernel version(s)?
> Is this expected behavior?
I'm not sure, but it sounds surprising.
> You can run the > tests/record_sample/mmap_multiple > test in the current git of my perf_event_tests testsuite for a testcase.
This appears to work for me:
nanook@ribbensteg:~/src/perf_event_tests/tests/record_sample$ ./mmap_multiple Trying to mmap same perf_event fd multiple times... PASSED
nanook@ribbensteg:~/src/perf_event_tests/tests/record_sample$ git log --oneline HEAD~1.. c82c4dd tests: huge_grou_start: add info that this was fixed in Linux 4.3 nanook@ribbensteg:~/src/perf_event_tests/tests/record_sample$ uname -a Linux ribbensteg 4.13.0-rc4-00010-g2ce1491 #229 SMP PREEMPT Thu Aug 10 17:06:56 BST 2017 aarch64 aarch64 aarch64 GNU/Linux
nanook@ribbensteg:~/src/perf_event_tests/tests/record_sample$ strace ./mmap_multiple execve("./mmap_multiple", ["./mmap_multiple"], [/* 18 vars */]) = 0 brk(0) = 0x2d9aa000 faccessat(AT_FDCWD, "/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xffff9d10e000 faccessat(AT_FDCWD, "/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=42361, ...}) = 0 mmap(NULL, 42361, PROT_READ, MAP_PRIVATE, 3, 0) = 0xffff9d103000 close(3) = 0 faccessat(AT_FDCWD, "/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0\267\0\1\0\0\0(\17\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1283776, ...}) = 0 mmap(NULL, 1356664, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xffff9cf9b000 mprotect(0xffff9d0ce000, 61440, PROT_NONE) = 0 mmap(0xffff9d0dd000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x132000) = 0xffff9d0dd000 mmap(0xffff9d0e3000, 13176, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xffff9d0e3000 close(3) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xffff9cf9a000 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xffff9cf99000 mprotect(0xffff9d0dd000, 16384, PROT_READ) = 0 mprotect(0x412000, 4096, PROT_READ) = 0 mprotect(0xffff9d112000, 4096, PROT_READ) = 0 munmap(0xffff9d103000, 42361) = 0 perf_event_open(0xfffffbff0310, 0, -1, -1, 0) = 3 mmap(NULL, 36864, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0xffff9d105000 mmap(NULL, 36864, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0xffff9cf90000 ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0 mmap(NULL, 65536, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xffff9cf80000 write(1, "Trying to mmap same perf_event f"..., 77Trying to mmap same perf_event fd multiple times... PASSED ) = 77 exit_group(0) = ? +++ exited with 0 +++
Thanks, Mark.
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