perf(agnocast_kmod): optimize exit worker and filter non-Agnocast PIDs#1083
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k1832 wants to merge 3 commits intotier4:mainfrom
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perf(agnocast_kmod): optimize exit worker and filter non-Agnocast PIDs#1083k1832 wants to merge 3 commits intotier4:mainfrom
k1832 wants to merge 3 commits intotier4:mainfrom
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The exit worker thread previously dequeued exactly one PID per wake-up cycle. When N processes exit simultaneously, this caused N separate sleep/wake context switches. Change to an inner drain loop that processes all queued PIDs before going back to sleep. Signed-off-by: Keita Morisaki <keita.morisaki@tier4.jp>
The kprobe on do_exit fires for every process exit system-wide. Previously, every exit — even unrelated processes — triggered the full enqueue/wake/dequeue/rwsem pipeline before being discarded in process_exit_cleanup. Add an RCU-protected hash lookup in the kprobe handler to skip non-Agnocast PIDs immediately (~50-100 ns) instead of going through the full pipeline (~6-14 us). This eliminates unnecessary rwsem acquisitions that contend with the publish/receive hot path. Changes: - Add rcu_head to process_info for deferred freeing - Use hash_add_rcu/hash_del_rcu/kfree_rcu for proc_info_htable - Use rcu_read_lock + hash_for_each_possible_rcu in kprobe handler - synchronize_rcu in remove_all_process_info at module exit Signed-off-by: Keita Morisaki <keita.morisaki@tier4.jp>
…apping Replace inline (EXIT_QUEUE_SIZE - 1) with a named EXIT_QUEUE_MASK constant. Remove the now-unnecessary comment about EXIT_QUEUE_SIZE being a power of two, since the mask definition makes this self-evident. Signed-off-by: Keita Morisaki <keita.morisaki@tier4.jp>
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Description
Three improvements to the process exit handling path:
Drain loop: The exit worker thread previously dequeued exactly one PID per wake-up cycle. When N processes exit simultaneously, this caused N separate sleep/wake context switches. Now all queued PIDs are drained in a single wake-up before going back to sleep.
RCU-based PID filtering: The kprobe on
do_exitfires for every process exit system-wide. Previously, every exit triggered the full enqueue → wake → dequeue → rwsem pipeline before being discarded inprocess_exit_cleanup. Now an RCU-protected hash lookup in the kprobe handler skips non-Agnocast PIDs immediately (~50-100 ns) instead of going through the full pipeline (~6-14 us). This eliminates unnecessary rwsem acquisitions that contend with the publish/receive hot path.EXIT_QUEUE_MASK: Replace inline
(EXIT_QUEUE_SIZE - 1)with a named constant.Related links
How was this PR tested?
bash scripts/e2e_test_1to1(required)bash scripts/e2e_test_2to2(required)Notes for reviewers
rcu_headtoprocess_infoand useshash_add_rcu/hash_del_rcu/kfree_rcuforproc_info_htable. This is a textbook RCU use case: a read-mostly hash table where writes are rare (process add/remove) and reads happen on every system-wide process exit.find_process_infoandprocess_exit_cleanupstill use non-RCU hash iteration underglobal_htables_rwsem, which provides sufficient synchronization. Only the kprobe handler (which cannot sleep) uses RCU.Version Update Label (Required)
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