Thanks for the reply, Stephane. I tried the test case you suggested:
main() {
int fd;
void *addr;
fd = open ("/tmp/foo", O_RDONLY);
printf("fd = %d\n", fd);
addr = mmap(NULL, 10, PROT_READ, MAP_PRIVATE, fd, 0);
printf("addr = %p\n", addr);
if (close(fd)) {
printf("close failed\n");
}
if (munmap(addr, 10)) {
printf("munmap failed\n");
}
}
and it worked fine. So apparently there is a problem related to
munmap'ing a perfmon fd on Power. This will need more investigation,
obviously.
- Corey
"stephane eranian" <eran...@googlemail.com> wrote on 01/06/2009 10:28:41
PM:
> Corey,
>
> On Wed, Jan 7, 2009 at 3:24 AM, Corey J Ashford <cjash...@us.ibm.com>
wrote:
> >
> > Hello,
> >
> > I'd appreciate it if someone on this mailing list could try out the
libpfm
> > example: task_smpl and see if it runs correctly for you on any other
> > architecture besides Power.
> >
> > When I run it on my Power5-based machine here, I get a system hang
that
> > occurs when the munmap call is made. Looking at the code in the
example, I
> > reversed the order of the close and munmap... so that the memory is
unmapped
> > before the fd is closed, and this allows the test to run to completion
> > without error and causes no hang. I also tried commenting out the
call to
> > pfm_start, to cut perfmon out of the loop for the most part, and the
> > behavior still reproduces - the system hangs unless I reverse those
two
> > calls.
> >
> > When the system hangs like this, if I get it to go into Xmon, none of
the
> > CPU stacks are interesting. They all appear to be idle.
> >
> > I run the test as follows:
> >
> > ./task_smpl /bin/sleep 3
> >
>
> This test runs fine on my x86-64 system (Core 2). The order of the
> close() vs munmap()
> should not matter. The calls can be made in any order. The perfmon
> context is destroyed
> when the last reference to the file descriptor disappears, mmap counts
> as 1. If you do close()
> followed by munmap(), the perfmon context is destroyed as part of the
> munmap(). This sequence
> should not hang for you. What happens if you do a similar sequence but
> just with a regular file:
> fd = open("/tmp/foo);
> addr = mmap(fd);
> close(fd);
> munmap(addr);
>
> The test runs to completion on both x86-64 and ia64:
>
> $ task_smpl /bin/sleep 3
> sycall base 295
> major version 2
> minor version 82
> [FIXED_CTRL(pmc16)=0xaa pmi0=1 en0=0x2 pmi1=1 en1=0x2 pmi2=1 en2=0x0]
> INSTRUCTIONS_RETIRED UNHALTED_CORE_CYCLES
> [FIXED_CTR0(pmd16)]
> [FIXED_CTR1(pmd17)]
> programming 1 PMCS and 2 PMDS
> buffer mapped @0x7f999029b000
> hdr_cur_offs=128 version=1.0
> task terminated
> entry 0 PID:32691 TID:32691 CPU:2 LAST_VAL:100000 IIP:0x7f66702246c2
> PMD16 :0x0000000000004130
> entry 1 PID:32691 TID:32691 CPU:2 LAST_VAL:100213 IIP:0x7f6670227560
> PMD16 :0x000000000000ef70
> entry 2 PID:32691 TID:32691 CPU:2 LAST_VAL:100060 IIP:0x7f6670233e52
> PMD16 :0x000000000000f384
> entry 3 PID:32691 TID:32691 CPU:2 LAST_VAL:100155 IIP:0xffffffff805c9e6f
> PMD16 :0x00000000000104fe
> 4 samples (4 in partial buffer) collected in 0 buffer overflows
> real 0h00m03.001s user 0h00m00.000s sys 0h00m00.001s
> $
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