Date: Fri, 01 Feb 2008 01:04:50 +0200 From: Alexander Motin <mav@FreeBSD.org> To: freebsd-performance@freebsd.org, freebsd-hackers@freebsd.org Subject: Memory allocation performance Message-ID: <47A25412.3010301@FreeBSD.org>
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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?
Thanks!
--
Alexander Motin
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