[Lustre-devel] COS performance issues

[Alex Zhuravlev]

would be good to look at profiles as the next one was ldlm_resource_get()

thanks, Alex

Alexander Zarochentsev wrote:
> On 8 October 2008 15:48:50 Alex Zhuravlev wrote:
>> try to profile with single CPU? you'll probably get an idea how
>> "per-cpu" approach can help.
> 
> I booted the MDS server with maxcpus=1 kernel parameter and here are the 
> results:
> 
> cos=0
> 2039.31 creates/sec (total: 2 threads 611794 creates 300 secs)
> 2037.80 creates/sec (total: 2 threads 611341 creates 300 secs)
> 2076.21 creates/sec (total: 2 threads 622864 creates 300 secs)
> 
> cos=1
> 1874.93 creates/sec (total: 2 threads 564354 creates 301 secs)
> 1923.97 creates/sec (total: 2 threads 577191 creates 300 secs)
> 1892.61 creates/sec (total: 2 threads 567783 creates 300 secs)
> 1874.74 creates/sec (total: 2 threads 562421 creates 300 secs)
> 
> unfortunately profiling info isn't available yet, the results are done 
> with SLES10 which can boot with maxcpus=1 but has no oprofile 
> installed.
> 
>> Alexander Zarochentsev wrote:
>>> I have a patch to avoid using of obd_uncommitted_replies_lock
>>> in ptlrpc_server_handle_reply but it has minimal effect,
>>> ptlrpc_server_handle_reply still the most cpu consuming function
>>> because of svc->srv_lock contention.
>>>
>>> I think the problem is that COS defers processing of replies to
>>> transaction commit time. When commit happens, MDS has to process
>>> thousands of replies (about 14k replies per commit in the test 3.a)
>>> in short period of time. I guess the mdt service threads all woken
>>> up and spin trying to get the service svr_lock. Processing of new
>>> requests may also suffer of this.
>>>
>>> I ran the tests with with CONFIG_DEBUG_SPINLOCK_SLEEP debugging
>>> compiled into a kernel, it found no sleep under spinlock bugs.
>>>
>>> Further optimization may include
>>> 1. per-reply spin locks.
>>> 2. per-cpu structures and threads to process reply queues.
>>>
>>> Any comments?
>>>
>>> Thanks.
>>>
>>> PS. the test results are much better when MDS server is sata20
>>> machine with 4 cores (the MDS from Washie1 has 2 cores), COS=0 and
>>> COS=1 have only %3 difference:
>>>
>>> COS=1
>>> Rate: 3101.77 creates/sec (total: 2 threads 930530 creates 300
>>> secs) Rate: 3096.94 creates/sec (total: 2 threads 929083 creates
>>> 300 secs)
>>>
>>> COS=0
>>> Rate: 3184.01 creates/sec (total: 2 threads 958388 creates 301
>>> secs) Rate: 3152.89 creates/sec (total: 2 threads 945868 creates
>>> 300 secs)
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>