15df03c879
For a custom microbenchmark on a 3.30GHz Xeon SandyBridge, which calls
IPC_STAT over and over, it was calculated that, on avg the cost of
ipc_get_maxid() for increasing amounts of keys was:
10 keys: ~900 cycles
100 keys: ~15000 cycles
1000 keys: ~150000 cycles
10000 keys: ~2100000 cycles
This is unsurprising as maxid is currently O(n).
By having the max_id available in O(1) we save all those cycles for each
semctl(_STAT) command, the idr_find can be expensive -- which some real
(customer) workloads actually poll on.
Note that this used to be the case, until commit
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| .. | ||
| compat.c | ||
| ipc_sysctl.c | ||
| Makefile | ||
| mq_sysctl.c | ||
| mqueue.c | ||
| msg.c | ||
| msgutil.c | ||
| namespace.c | ||
| sem.c | ||
| shm.c | ||
| syscall.c | ||
| util.c | ||
| util.h | ||