Robert Watson wrote:
Hence my request for drilling down a bit on profiling -- the question
I'm asking is whether profiling shows things running or taking time that
shouldn't be.
I have not yet understood why does it happend, but hwpmc shows huge
amount of "p4-resource-stall"s in UMA functions:
% cumulative self self total
time seconds seconds calls ms/call ms/call name
45.2 2303.00 2303.00 0 100.00% uma_zfree_arg [1]
41.2 4402.00 2099.00 0 100.00% uma_zalloc_arg [2]
1.4 4472.00 70.00 0 100.00%
uma_zone_exhausted_nolock [3]
0.9 4520.00 48.00 0 100.00% ng_snd_item [4]
0.8 4562.00 42.00 0 100.00% __qdivrem [5]
0.8 4603.00 41.00 0 100.00% ether_input [6]
0.6 4633.00 30.00 0 100.00% ng_ppp_prepend [7]
Probably it explains why "p4-global-power-events" shows many hits into them
% cumulative self self total
time seconds seconds calls ms/call ms/call name
20.0 37984.00 37984.00 0 100.00% uma_zfree_arg [1]
17.8 71818.00 33834.00 0 100.00% uma_zalloc_arg [2]
4.0 79483.00 7665.00 0 100.00% ng_snd_item [3]
3.0 85256.00 5773.00 0 100.00% __mcount [4]
2.3 89677.00 4421.00 0 100.00% bcmp [5]
2.2 93853.00 4176.00 0 100.00% generic_bcopy [6]
, while "p4-instr-retired" does not.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
11.1 5351.00 5351.00 0 100.00% ng_apply_item [1]
7.9 9178.00 3827.00 0 100.00%
legacy_pcib_alloc_msi [2]
4.1 11182.00 2004.00 0 100.00% init386 [3]
4.0 13108.00 1926.00 0 100.00% rn_match [4]
3.5 14811.00 1703.00 0 100.00% uma_zalloc_arg [5]
2.6 16046.00 1235.00 0 100.00% SHA256_Transform [6]
2.2 17130.00 1084.00 0 100.00% ng_add_hook [7]
2.0 18111.00 981.00 0 100.00% ng_rmhook_self [8]
2.0 19054.00 943.00 0 100.00% em_encap [9]
For this moment I have invent two possible explanation. One is that due
to UMA's cyclic block allocation order it does not fits CPU caches and
another that it is somehow related to critical_exit(), which possibly
can cause context switch. Does anybody have better explanation how such
small and simple in this part function can cause such results?
--
Alexander Motin
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