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ipc: optimize semget/shmget/msgget for lots of keys

Browse source 
ipc_findkey() used to scan all objects to look for the wanted key.  This
is slow when using a high number of keys.  This change adds an rhashtable
of kern_ipc_perm objects in ipc_ids, so that one lookup cease to be O(n).

This change gives a 865% improvement of benchmark reaim.jobs_per_min on a
56 threads Intel(R) Xeon(R) CPU E5-2695 v3 @ 2.30GHz with 256G memory [1]

Other (more micro) benchmark results, by the author: On an i5 laptop, the
following loop executed right after a reboot took, without and with this
change:

    for (int i = 0, k=0x424242; i < KEYS; ++i)
        semget(k++, 1, IPC_CREAT | 0600);

                 total       total          max single  max single
   KEYS        without        with        call without   call with

      1            3.5         4.9   µs            3.5         4.9
     10            7.6         8.6   µs            3.7         4.7
     32           16.2        15.9   µs            4.3         5.3
    100           72.9        41.8   µs            3.7         4.7
   1000        5,630.0       502.0   µs             *           *
  10000    1,340,000.0     7,240.0   µs             *           *
  31900   17,600,000.0    22,200.0   µs             *           *

 *: unreliable measure: high variance

The duration for a lookup-only usage was obtained by the same loop once
the keys are present:

                 total       total          max single  max single
   KEYS        without        with        call without   call with

      1            2.1         2.5   µs            2.1         2.5
     10            4.5         4.8   µs            2.2         2.3
     32           13.0        10.8   µs            2.3         2.8
    100           82.9        25.1   µs             *          2.3
   1000        5,780.0       217.0   µs             *           *
  10000    1,470,000.0     2,520.0   µs             *           *
  31900   17,400,000.0     7,810.0   µs             *           *

Finally, executing each semget() in a new process gave, when still
summing only the durations of these syscalls:

creation:
                 total       total
   KEYS        without        with

      1            3.7         5.0   µs
     10           32.9        36.7   µs
     32          125.0       109.0   µs
    100          523.0       353.0   µs
   1000       20,300.0     3,280.0   µs
  10000    2,470,000.0    46,700.0   µs
  31900   27,800,000.0   219,000.0   µs

lookup-only:
                 total       total
   KEYS        without        with

      1            2.5         2.7   µs
     10           25.4        24.4   µs
     32          106.0        72.6   µs
    100          591.0       352.0   µs
   1000       22,400.0     2,250.0   µs
  10000    2,510,000.0    25,700.0   µs
  31900   28,200,000.0   115,000.0   µs

[1] http://lkml.kernel.org/r/20170814060507.GE23258@yexl-desktop

Link: http://lkml.kernel.org/r/20170815194954.ck32ta2z35yuzpwp@debix
Signed-off-by: Guillaume Knispel <[email protected]>
Reviewed-by: Marc Pardo <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Manfred Spraul <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: "Peter Zijlstra (Intel)" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Serge Hallyn <[email protected]>
Cc: Andrey Vagin <[email protected]>
Cc: Guillaume Knispel <[email protected]>
Cc: Marc Pardo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Guillaume Knispel 2017-09-08 16:17:55 -07:00 • committed by Linus Torvalds
commit 0cfb6aee70
8 changed files with 130 additions and 50 deletions
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21
ipc/util.h
View file

@ -15,8 +15,8 @@
#define SEQ_MULTIPLIER (IPCMNI)
void sem_init(void);
void msg_init(void);
int sem_init(void);
int msg_init(void);
void shm_init(void);
struct ipc_namespace;
@ -30,17 +30,17 @@ static inline void mq_put_mnt(struct ipc_namespace *ns) { }
#endif
#ifdef CONFIG_SYSVIPC
void sem_init_ns(struct ipc_namespace *ns);
void msg_init_ns(struct ipc_namespace *ns);
void shm_init_ns(struct ipc_namespace *ns);
int sem_init_ns(struct ipc_namespace *ns);
int msg_init_ns(struct ipc_namespace *ns);
int shm_init_ns(struct ipc_namespace *ns);
void sem_exit_ns(struct ipc_namespace *ns);
void msg_exit_ns(struct ipc_namespace *ns);
void shm_exit_ns(struct ipc_namespace *ns);
#else
static inline void sem_init_ns(struct ipc_namespace *ns) { }
static inline void msg_init_ns(struct ipc_namespace *ns) { }
static inline void shm_init_ns(struct ipc_namespace *ns) { }
static inline int sem_init_ns(struct ipc_namespace *ns) { return 0; }
static inline int msg_init_ns(struct ipc_namespace *ns) { return 0; }
static inline int shm_init_ns(struct ipc_namespace *ns) { return 0; }
static inline void sem_exit_ns(struct ipc_namespace *ns) { }
static inline void msg_exit_ns(struct ipc_namespace *ns) { }
@ -79,7 +79,7 @@ struct ipc_ops {
struct seq_file;
struct ipc_ids;
void ipc_init_ids(struct ipc_ids *);
int ipc_init_ids(struct ipc_ids *);
#ifdef CONFIG_PROC_FS
void __init ipc_init_proc_interface(const char *path, const char *header,
int ids, int (*show)(struct seq_file *, void *));
@ -104,6 +104,9 @@ int ipc_get_maxid(struct ipc_ids *);
/* must be called with both locks acquired. */
void ipc_rmid(struct ipc_ids *, struct kern_ipc_perm *);
/* must be called with both locks acquired. */
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);