On 09/11/2015 07:13 PM, Davidlohr Bueso wrote:
On Fri, 11 Sep 2015, Waiman Long wrote:
A sample of statistics counts after system bootup (with vCPU
overcommit) was:
hash_hops_count=9001
kick_latencies=138047878
kick_unlock_count=9001
kick_wait_count=9000
spurious_wakeup=3
wait_again_count=2
wait_head_count=10
wait_node_count=8994
wake_latencies=713195944
Any reason you chose not to make the stats per-cpu? The locking
numbers don't have to be exact, so you can easily get away with
it and suffer from much less overhead that resorting to atomics.
Obviously assuming that reading/collecting the stats is done
infrequently, such as between workloads or at bootup as you did.
Thanks,
Davidlohr
You can't use debugfs if we want to have per-cpu stats. We will have to
use sysfs instead. This will require more code changes. It is certainly
doable, but we have to choose between simplicity and performance
overhead. Right now, I am assuming that lock PV lockstat is used
primarily for debugging purpose and won't be enabled on production
system. If we want to have this capability in production systems, we
will certainly need to change it to per-cpu stats and use sysfs instead.
The original PV ticketlock code used debugfs and I was just following
its footstep. Do you think it is worthwhile to have this capability
available on production system by default?
Cheers,
Longman
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