Memory allocation performance

[Alexander Motin]

Julian Elischer пишет:
> Alexander Motin wrote:
>> Hi.
>>
>> While profiling netgraph operation on UP HEAD router I have found that 
>> huge amount of time it spent on memory allocation/deallocation:
>>
>>         0.14  0.05  132119/545292      ip_forward <cycle 1> [12]
>>         0.14  0.05  133127/545292      fxp_add_rfabuf [18]
>>         0.27  0.10  266236/545292      ng_package_data [17]
>> [9]14.1 0.56  0.21  545292         uma_zalloc_arg [9]
>>         0.17  0.00  545292/1733401     critical_exit <cycle 2> [98]
>>         0.01  0.00  275941/679675      generic_bzero [68]
>>         0.01  0.00  133127/133127      mb_ctor_pack [103]
>>
>>         0.15  0.06  133100/545266      mb_free_ext [22]
>>         0.15  0.06  133121/545266      m_freem [15]
>>         0.29  0.11  266236/545266      ng_free_item [16]
>> [8]15.2 0.60  0.23  545266         uma_zfree_arg [8]
>>         0.17  0.00  545266/1733401     critical_exit <cycle 2> [98]
>>         0.00  0.04  133100/133100      mb_dtor_pack [57]
>>         0.00  0.00  134121/134121      mb_dtor_mbuf [111]
>>
>> I have already optimized all possible allocation calls and those that 
>> left are practically unavoidable. But even after this kgmon tells that 
>> 30% of CPU time consumed by memory management.
>>
>> So I have some questions:
>> 1) Is it real situation or just profiler mistake?
>> 2) If it is real then why UMA is so slow? I have tried to replace it 
>> in some places with preallocated TAILQ of required memory blocks 
>> protected by mutex and according to profiler I have got _much_ better 
>> results. Will it be a good practice to replace relatively small UMA 
>> zones with preallocated queue to avoid part of UMA calls?
>> 3) I have seen that UMA does some kind of CPU cache affinity, but does 
>> it cost so much that it costs 30% CPU time on UP router?
> 
> given this information, I would add an 'item cache' in ng_base.c
> (hmm do I already have one?)

That was actually my second question. As there is only 512 items by 
default and they are small in size I can easily preallocate them all on 
boot. But is it a good way? Why UMA can't do just the same when I have 
created zone with specified element size and maximum number of objects? 
What is the principal difference?

-- 
Alexander Motin