On 02/22/2015 11:09 PM, Gregory Farnum wrote:
On Tue, Feb 17, 2015 at 9:37 AM, Mark Nelson <mnelson@xxxxxxxxxx> wrote:
Hi All,
I wrote up a short document describing some tests I ran recently to look at
how SSD backed OSD performance has changed across our LTS releases. This is
just looking at RADOS performance and not RBD or RGW. It also doesn't offer
any real explanations regarding the results. It's just a first high level
step toward understanding some of the behaviors folks on the mailing list
have reported over the last couple of releases. I hope you find it useful.
Do you have any work scheduled to examine the synchronous IO latency
changes across versions? I suspect those are involved with the loss of
performance some users have reported, and I've not heard any
believable theories as to the cause. Since this is the first set of
results pointing that way on hardware available for detailed tests I
hope we can dig into it. And those per-op latencies are the next thing
we'll need to cut down on, since they correspond pretty directly with
CPU costs that we want to scale down! :)
I kind of suspect that some of the user issues might be RBD on the
client side (or even QEMU). Certainly possible it's OSD too though.
With so many different kinds of hardware and so many ways to tune things
it can be tough to narrow down. I'm really looking forward to the work
that's being done on LTTNG tracing. That will give us much easier
insight into these kinds of things than we've had in the past.
-Greg
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