On 11/14/2019 12:17 PM, William Brown wrote:
> On 14 Nov 2019, at 19:06, Ludwig Krispenz <lkrispen(a)redhat.com> wrote:
>
>
> On 11/14/2019 09:29 AM, William Brown wrote:
>>> On 14 Nov 2019, at 18:22, Ludwig Krispenz <lkrispen(a)redhat.com> wrote:
>>>
>>> Hi William,
>>>
>>> before further thinking about this, I need some clarification, or maybe I
just missed this. When you talk about 1..16 threads do you mean worker threads ?
>> Server worker threads. ldclt is set to only use 10 client threads - which is
surprising that with 10 client threads we see a decline when workers > 10 (one would
assume it should stabilise).
>>
>>> Or concurrent client connection threads in ldclt/rsearch/.... - how many
concurrent connections do you have and how does varying this number change results ?
>> I will add more tests to this to allow varying the ldclt numbers.
> ok, and I assume that you are using a version with nunc-stans removed, could you
please also verify the effect of tubo-mode on/off ?
Correct, I'm using git master. Yes I'll check that also. I plan to add
permutations like this to the test harness so it's easier for us to repeat in the
future when we make changes.
I also need to find a way to wire in perf/stap so we can generate flamegraphs from each
test run too for later analysis.
Thanks for the great ideas :)
Thanks, and one more idea ;-)
Can you separate the client and the server on two different machines,
I've seen ldclt or other clients impacting cpu usage a lot, there will
be some network overhead, but this should be ok (and more realistic)
>>> Regards,
>>> Ludwig
>>>
>>> On 11/14/2019 03:34 AM, William Brown wrote:
>>>> Hi all,
>>>>
>>>> After our catch up, we were discussing performance matters. I decided to
start on this while waiting for some of my tickets to be reviewed and to see what's
going on.
>>>>
>>>> These tests were carried out on a virtual machine configured in search 6
to have access to 6 CPU's, and search 12 with 12 CPU. Both machines had access to 8GB
of ram.
>>>>
>>>> The hardware is an i7 2.2GHz with 6 cores (12 threads) and 32GB of ram,
with NVME storage provided.
>>>>
>>>> The rows are the VM CPU's available, and the columns are the number
of threads in nsslapd-threadnumber. No other variables were changed. The database has 6000
users and 4000 groups. The instance was restarted before each test. The search was a
randomised uid equality test with a single result. I provided the thread 6 and 12 columns
to try to match the VM and host specs rather than just the traditional base 2 sequence we
see.
>>>>
>>>> I've attached a screen shot of the results, but I have some initial
thoughts to provide on this. What's interesting is our initial 1 thread performance
and how steeply it ramps up towards 4 thread. This in mind it's not a linear increase.
Per thread on s6 we go from ~3800 to ~2500 ops per second, and a similar ratio exists in
s12. What is stark is that after t4 we immediately see a per thread *decline* despite the
greater amount of available computer resources. This indicates that it is poor locking and
thread coordination causing a rapid decline in performance. This was true on both s6 and
s12. The decline intesifies rapidly once we exceed the CPU avail on the host (s6 between
t6 to t12), but still declines even when we do have the hardware threads available in
s12.
>>>>
>>>> I will perform some testing between t1 and t6 versions to see if I can
isolate which functions are having a growth in time consumption.
>>>>
>>>> For now an early recommendation is that we alter our default CPU
auto-tuning. Currently we use a curve which starts at 16 threads from 1 to 4 cores, and
then tapering down to 512 cores to 512 threads - however in almost all of these autotuned
threads we have threads greater than our core count. This from this graph would indicate
that this decision only hurts our performance rather than improving it. I suggest we
change our thread autotuning to be 1 to 1 ratio of threads to cores to prevent over
contention on lock resources.
>>>>
>>>> Thanks, more to come once I setup this profiling on a real machine so I
can generate flamegraphs.
>>>>
>>>> <Mail Attachment.png>
>>>>
>>>> —
>>>> Sincerely,
>>>>
>>>> William Brown
>>>>
>>>> Senior Software Engineer, 389 Directory Server
>>>> SUSE Labs
>>>>
>>>>
>>>>
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>> —
>> Sincerely,
>>
>> William Brown
>>
>> Senior Software Engineer, 389 Directory Server
>> SUSE Labs
>> _______________________________________________
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Shander
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—
Sincerely,
William Brown
Senior Software Engineer, 389 Directory Server
SUSE Labs
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