On 1 Jun 2017, at 11:48, Jeff Layton wrote:
On Thu, 2017-06-01 at 11:14 -0400, J. Bruce Fields wrote:
On Thu, Jun 01, 2017 at 08:59:21AM -0400, Jeff Layton wrote:
I'm not so sure. That would only be the case if the thing were
marked
for manadatory locking (a really rare thing).
The test is really simple and I don't think any read/write activity
is
involved:
https://github.com/antonblanchard/will-it-scale/blob/master/tests/lock1.c
So it's just F_WRLCK/F_UNLCK in a loop spread across multiple cores?
I'd think real workloads do some work while holding the lock, and a
15%
regression on just the pure lock/unlock loop might not matter? But
best
to be careful, I guess.
--b.
Yeah, that's my take.
I was assuming that getting a pid reference would be essentially free,
but it doesn't seem to be.
So, I think we probably want to avoid taking it for a file_lock that
we
use to request a lock, but do take it for a file_lock that is used to
record a lock. How best to code that up, I'm not quite sure...
Maybe as simple as only setting fl_nspid in locks_insert_lock_ctx(), but
that seems to just take us back to the problem of getting the pid wrong
if
the lock is inserted later by a different worker than created the
request.
I have a mind now to just drop fl_nspid off the struct file_lock
completely,
and instead just carry fl_pid, and when we do F_GETLK, we can do:
task = find_task_by_pid_ns(fl_pid, init_pid_ns)
fl_nspid = task_pid_nr_ns(task, task_active_pid_ns(current))
That moves all the work off into the F_GETLK case, which I think is not
used
so much.
Ben
