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authorDavidlohr Bueso <dave@stgolabs.net>2017-11-17 15:31:18 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-11-17 16:10:04 -0800
commit15df03c87983660a4d1eedb4541778592bd97684 (patch)
treefb8e7ae25cee35177eb45e11bb3435f79ccc009f /ipc/util.c
parentsysvipc: properly name ipc_addid() limit parameter (diff)
downloadlinux-dev-15df03c87983660a4d1eedb4541778592bd97684.tar.xz
linux-dev-15df03c87983660a4d1eedb4541778592bd97684.zip
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 'ipc/util.c')
-rw-r--r--ipc/util.c43
1 files changed, 13 insertions, 30 deletions
diff --git a/ipc/util.c b/ipc/util.c
index e09bf76610ef..ff045fec8d83 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -122,6 +122,7 @@ int ipc_init_ids(struct ipc_ids *ids)
return err;
idr_init(&ids->ipcs_idr);
ids->tables_initialized = true;
+ ids->max_id = -1;
#ifdef CONFIG_CHECKPOINT_RESTORE
ids->next_id = -1;
#endif
@@ -188,36 +189,6 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
return NULL;
}
-/**
- * ipc_get_maxid - get the last assigned id
- * @ids: ipc identifier set
- *
- * Called with ipc_ids.rwsem held.
- */
-int ipc_get_maxid(struct ipc_ids *ids)
-{
- struct kern_ipc_perm *ipc;
- int max_id = -1;
- int total, id;
-
- if (ids->in_use == 0)
- return -1;
-
- if (ids->in_use == IPCMNI)
- return IPCMNI - 1;
-
- /* Look for the last assigned id */
- total = 0;
- for (id = 0; id < IPCMNI && total < ids->in_use; id++) {
- ipc = idr_find(&ids->ipcs_idr, id);
- if (ipc != NULL) {
- max_id = id;
- total++;
- }
- }
- return max_id;
-}
-
#ifdef CONFIG_CHECKPOINT_RESTORE
/*
* Specify desired id for next allocated IPC object.
@@ -313,6 +284,9 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
}
ids->in_use++;
+ if (id > ids->max_id)
+ ids->max_id = id;
+
new->id = ipc_buildid(id, ids, new);
return id;
@@ -459,6 +433,15 @@ void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
ipc_kht_remove(ids, ipcp);
ids->in_use--;
ipcp->deleted = true;
+
+ if (unlikely(lid == ids->max_id)) {
+ do {
+ lid--;
+ if (lid == -1)
+ break;
+ } while (!idr_find(&ids->ipcs_idr, lid));
+ ids->max_id = lid;
+ }
}
/**