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Commit6dd4142fb5("Merge branch 'af_unix-per-netns-socket-hash'") and commit51bae889fe("af_unix: Put pathname sockets in the global hash table.") changed a hash table layout. Before: unix_socket_table [0 - 255] : abstract & pathname sockets [256 - 511] : unnamed sockets After: per-netns table [0 - 255] : abstract & pathname sockets [256 - 511] : unnamed sockets bsd_socket_table [0 - 255] : pathname sockets (sk_bind_node) Now, while looking up sockets, we traverse the global table for the pathname sockets and the first half of each per-netns hash table for abstract sockets, where pathname sockets are also linked. Thus, the more pathname sockets we have, the longer we take to look up abstract sockets. This characteristic has been there before the layout change, but we can improve it now. This patch changes the per-netns hash table's layout so that sockets not requiring lookup reside in the first half and do not impact the lookup of abstract sockets. per-netns table [0 - 255] : pathname & unnamed sockets [256 - 511] : abstract sockets bsd_socket_table [0 - 255] : pathname sockets (sk_bind_node) We have run a test that bind()s 100,000 abstract/pathname sockets for each, bind()s an abstract socket 100,000 times and measures the time on __unix_find_socket_byname(). The result shows that the patch makes each lookup faster. Without this patch: $ sudo ./funclatency -p 2278 --microseconds __unix_find_socket_byname.isra.44 usec : count distribution 0 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 126 | | 16 -> 31 : 1438 |* | 32 -> 63 : 4150 |*** | 64 -> 127 : 9049 |******* | 128 -> 255 : 37704 |******************************* | 256 -> 511 : 47533 |****************************************| With this patch: $ sudo ./funclatency -p 3648 --microseconds __unix_find_socket_byname.isra.46 usec : count distribution 0 -> 1 : 109 | | 2 -> 3 : 318 | | 4 -> 7 : 725 | | 8 -> 15 : 2501 |* | 16 -> 31 : 3061 |** | 32 -> 63 : 4028 |*** | 64 -> 127 : 9312 |******* | 128 -> 255 : 51372 |****************************************| 256 -> 511 : 28574 |********************** | Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://lore.kernel.org/r/20220705233715.759-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Linux kernel
============
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