On Mon, Dec 1, 2014 at 6:25 PM, Linus Torvalds
<torva...@linux-foundation.org> wrote:
On Mon, Dec 1, 2014 at 3:08 PM, Chris Mason <c...@fb.com> wrote:
I'm not sure if this is related, but running trinity here, I
noticed it
was stuck at 100% system time on every CPU. perf report tells me
we are
spending all of our time in spin_lock under the sync system call.
I think it's coming from contention in the bdi_queue_work() call
from
inside sync_inodes_sb, which is spin_lock_bh().
Please do a perf run with -g to get the call chain to make sure..
The call chain goes something like this:
--- _raw_spin_lock
|
|--99.72%-- sync_inodes_sb
| sync_inodes_one_sb
| iterate_supers
| sys_sync
| |
| |--79.66%-- system_call_fastpath
| | syscall
| |
| --20.34%-- ia32_sysret
| __do_syscall
--0.28%-- [...]
(the 64bit call variation is similar) Adding -v doesn't really help,
because it isn't giving me the address inside sync_inodes_sb()
I first read this and guessed it must be leaving out the call to
bdi_queue_work, hoping the spin_lock_bh and lock debugging were teaming
up to stall the box.
But looking harder it's probably inside wait_sb_inodes:
spin_lock(&inode_sb_list_lock);
Which is a little harder to blame. Maaaaaybe with lock debugging, but
its enough of a stretch that I wouldn't have emailed at all if I hadn't
fixated on the bdi code.
-chris
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