diff options
author | Davidlohr Bueso <dave@stgolabs.net> | 2017-11-18 00:31:18 +0100 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-11-18 01:10:04 +0100 |
commit | 15df03c87983660a4d1eedb4541778592bd97684 (patch) | |
tree | fb8e7ae25cee35177eb45e11bb3435f79ccc009f /ipc | |
parent | sysvipc: properly name ipc_addid() limit parameter (diff) | |
download | linux-15df03c87983660a4d1eedb4541778592bd97684.tar.xz linux-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')
-rw-r--r-- | ipc/util.c | 43 | ||||
-rw-r--r-- | ipc/util.h | 21 |
2 files changed, 31 insertions, 33 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; + } } /** diff --git a/ipc/util.h b/ipc/util.h index 0cd6201fe63a..89b8ec176fc4 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -13,6 +13,7 @@ #include <linux/unistd.h> #include <linux/err.h> +#include <linux/ipc_namespace.h> #define SEQ_MULTIPLIER (IPCMNI) @@ -99,9 +100,6 @@ void __init ipc_init_proc_interface(const char *path, const char *header, /* must be called with ids->rwsem acquired for writing */ int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int); -/* must be called with ids->rwsem acquired for reading */ -int ipc_get_maxid(struct ipc_ids *); - /* must be called with both locks acquired. */ void ipc_rmid(struct ipc_ids *, struct kern_ipc_perm *); @@ -111,6 +109,23 @@ void ipc_set_key_private(struct ipc_ids *, struct kern_ipc_perm *); /* must be called with ipcp locked */ int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flg); +/** + * ipc_get_maxid - get the last assigned id + * @ids: ipc identifier set + * + * Called with ipc_ids.rwsem held for reading. + */ +static inline int ipc_get_maxid(struct ipc_ids *ids) +{ + if (ids->in_use == 0) + return -1; + + if (ids->in_use == IPCMNI) + return IPCMNI - 1; + + return ids->max_id; +} + /* * For allocation that need to be freed by RCU. * Objects are reference counted, they start with reference count 1. |