[tor-bugs] #7727 [Tor]: Simplify some costly Tor functions (by profile)

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#7727: Simplify some costly Tor functions (by profile)
-----------------------+----------------------------------------------------
 Reporter:  nickm      |          Owner:                    
     Type:  defect     |         Status:  new               
 Priority:  normal     |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor        |        Version:  Tor: 0.2.4.6-alpha
 Keywords:  tor-relay  |         Parent:                    
   Points:             |   Actualpoints:                    
-----------------------+----------------------------------------------------
 mo attached a few profiles to #7572, from a fast host with aesni  The top
 functions overall are are:

 {{{
 44222784  8.0379  libcrypto.so.1.0.0       libcrypto.so.1.0.0
 sha1_block_data_order_avx
 39059344  7.0994  nf_conntrack             nf_conntrack
 /nf_conntrack
 35552271  6.4620  libcrypto.so.1.0.0       libcrypto.so.1.0.0
 bn_sqr4x_mont
 31025085  5.6391  libcrypto.so.1.0.0       libcrypto.so.1.0.0
 aesni_cbc_sha1_enc_avx
 17425081  3.1672  tor                      tor
 circuit_get_by_rend_token_and_purpose.constprop.11
 17185351  3.1236  libc-2.15.so             libc-2.15.so
 /lib/x86_64-linux-gnu/libc-2.15.so
 15106522  2.7458  tor                      tor
 circuit_unlink_all_from_channel
 13422467  2.4397  libevent-2.0.so.5.1.4    libevent-2.0.so.5.1.4
 /usr/lib/libevent-2.0.so.5.1.4
 9045536   1.6441  libcrypto.so.1.0.0       libcrypto.so.1.0.0
 bn_mul4x_mont_gather5
 8295787   1.5078  libcrypto.so.1.0.0       libcrypto.so.1.0.0
 aesni_ctr32_encrypt_blocks
 7454822   1.3550  e1000e                   e1000e
 /e1000e
 6667075   1.2118  tor                      tor
 circuitmux_find_map_entry
 }}}

 And the top functions, considering Tor only, are:
 {{{
 17545411 13.9182  circuitlist.c:1116          tor
 circuit_get_by_rend_token_and_purpose.constprop.11
 15232931 12.0838  circuitlist.c:1028          tor
 circuit_unlink_all_from_channel
 6729424   5.3382  circuitmux.c:698            tor
 circuitmux_find_map_entry
 3802661   3.0165  buffers.c:2468              tor
 assert_buf_ok
 3344356   2.6530  circuitlist.c:980           tor
 circuit_get_by_circid_channel
 3217962   2.5527  relay.c:2094                tor
 channel_flush_from_first_active_circuit
 2927776   2.3225  buffers.c:520               tor
 buf_datalen
 2367670   1.8782  connection.c:2512           tor
 connection_bucket_refill
 2210529   1.7535  connection.c:2824           tor
 connection_handle_read
 2200952   1.7459  relay.c:168                 tor
 circuit_receive_relay_cell
 2095244   1.6621  container.c:167             tor
 smartlist_isin
 1618112   1.2836  crypto.c:1364               tor
 crypto_cipher_crypt_inplace
 }}}

 The crypto's about what we'd expect, but it could be helpful to see if we
 can optimize some of the remaining Tor things.  In particular:
  * circuit_get_by_rend_token_and_purpose should have a map backing it; it
 appears that this might be one of those '''costly''' linear searches.
  * I wonder if circuit_unlink_all_from_channel could be taught to walk a
 list of circuits on the channel rather than the list of all circuits.
  * I don't see a good way to make circuitmux_find_map_entry faster without
 tweaking data structures.
  * assert_buf_ok(), we can call less.
  * circuit_get_by_circid_channel would also need data structure
 impreovements.
  * buf_datalen() should just be made into an inline function.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7727>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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