diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2017-11-17 15:31:18 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-11-17 16:10:04 -0800 |
| commit | 15df03c87983660a4d1eedb4541778592bd97684 (patch) | |
| tree | fb8e7ae25cee35177eb45e11bb3435f79ccc009f /include | |
| parent | ebf66799acfb5f52ada4ff96ecc9579867941ea9 (diff) | |
| download | linux-15df03c87983660a4d1eedb4541778592bd97684.tar.bz2 | |
sysvipc: make get_maxid O(1) again
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 7ca7e564e04 ("ipc:
store ipcs into IDRs"). The cost is the extra idr_find when doing
RMIDs, but we simply go backwards, and should not take too many
iterations to find the new value.
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170831172049.14576-5-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/ipc_namespace.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index d7cf3a850853..b5630c8eb2f3 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -19,6 +19,7 @@ struct ipc_ids { bool tables_initialized; struct rw_semaphore rwsem; struct idr ipcs_idr; + int max_id; #ifdef CONFIG_CHECKPOINT_RESTORE int next_id; #endif |