On 05/10/2017 05:31 PM, Jason Dillaman wrote:
On Wed, May 10, 2017 at 6:10 PM, Mark Nelson <mnelson@xxxxxxxxxx> wrote:
1) 7 - tp_librbd, line 82
Lots of stuff going on here, but the big thing is all the time spent in
librbd::ImageCtx::write_to_cache. 70.2% of the total time in this thread is
spent in ObjectCacher::writex with lots of nested stuff, but if you look all
the way down on line 1293, another 11.8% of the time is spent in Locker()
and 1.5% of the time spent in ~Locker().
Yes -- the ObjectCacher is long overdue for a re-write since it's
single threaded. It looks like you were essentially performing
writethrough as well. I'd imagine you would just be better off
disabling the rbd cache when doing high-performance random write
workloads since you are going to get zero benefit from the cache with
that workload -- at least that's what I usually recommend.
Often I do turn rbd cache off for bluestore testing. This was an older
conf file where I inadvertently hadn't disabled it. Still, it's an
unfortunate choice that has to be made, potentially by someone other
than the user running the workload. :/
Mark
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