On 12/16/2014 08:52 PM, Elliott, Robert (Server Storage) wrote:
(gdb) thread 2
[Switching to thread 2 (Thread 0x7fa92bf87700 (LWP 6733))]#0 0x0000003657600667 in io_submit () from /lib64/libaio.so.1
(gdb) bt
#0 0x0000003657600667 in io_submit () from /lib64/libaio.so.1
#1 0x0000000000457058 in fio_libaio_commit (td=0x7fa9a0dd1860) at engines/libaio.c:255
#2 0x000000000040b395 in td_io_commit (td=0x7fa9a0dd1860) at ioengines.c:396
#3 0x000000000040bea1 in td_io_queue (td=0x7fa9a0dd1860, io_u=0x7fa8e401c980) at ioengines.c:343
#4 0x000000000044a75d in do_io (td=0x7fa9a0dd1860) at backend.c:792
#5 0x000000000044c209 in thread_main (data=0x7fa9a0dd1860) at backend.c:1504
#6 0x0000003974c079d1 in start_thread () from /lib64/libpthread.so.0
#7 0x00000039748e8b7d in clone () from /lib64/libc.so.6
(gdb) print td
No symbol "td" in current context.
(gdb) select-frame 5
(gdb) print td->tv_cache
$51 = {tv_sec = 1099511, tv_usec = 641885}
^^^^^^^
This is the key. If this multiplication overflows:
usecs = (t * inv_cycles_per_usec) / 16777216UL;
then usecs is 2^64/2^24, which is 1099511627776. Divide that by 10^6 to
get seconds, and that is 1099511... I initially thought this was a buggy
backwards timer, but it's just this overflow. Fix:
http://git.kernel.dk/?p=fio.git;a=commit;h=b3fa625b38a638cd1783e9fdcac1b958e37e48fa
--
Jens Axboe
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