From 0cfb6aee70bddbef6ec796b255f588ce0e126766 Mon Sep 17 00:00:00 2001 From: Guillaume Knispel Date: Fri, 8 Sep 2017 16:17:55 -0700 Subject: ipc: optimize semget/shmget/msgget for lots of keys MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Marc Pardo Cc: Davidlohr Bueso Cc: Kees Cook Cc: Manfred Spraul Cc: Alexey Dobriyan Cc: "Eric W. Biederman" Cc: "Peter Zijlstra (Intel)" Cc: Ingo Molnar Cc: Sebastian Andrzej Siewior Cc: Serge Hallyn Cc: Andrey Vagin Cc: Guillaume Knispel Cc: Marc Pardo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/shm.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) (limited to 'ipc/shm.c') diff --git a/ipc/shm.c b/ipc/shm.c index 8828b4c..8fc97be 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -72,14 +72,14 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp); static int sysvipc_shm_proc_show(struct seq_file *s, void *it); #endif -void shm_init_ns(struct ipc_namespace *ns) +int shm_init_ns(struct ipc_namespace *ns) { ns->shm_ctlmax = SHMMAX; ns->shm_ctlall = SHMALL; ns->shm_ctlmni = SHMMNI; ns->shm_rmid_forced = 0; ns->shm_tot = 0; - ipc_init_ids(&shm_ids(ns)); + return ipc_init_ids(&shm_ids(ns)); } /* @@ -95,7 +95,7 @@ static void do_shm_rmid(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) if (shp->shm_nattch) { shp->shm_perm.mode |= SHM_DEST; /* Do not find it any more */ - shp->shm_perm.key = IPC_PRIVATE; + ipc_set_key_private(&shm_ids(ns), &shp->shm_perm); shm_unlock(shp); } else shm_destroy(ns, shp); @@ -106,13 +106,15 @@ void shm_exit_ns(struct ipc_namespace *ns) { free_ipcs(ns, &shm_ids(ns), do_shm_rmid); idr_destroy(&ns->ids[IPC_SHM_IDS].ipcs_idr); + rhashtable_destroy(&ns->ids[IPC_SHM_IDS].key_ht); } #endif static int __init ipc_ns_init(void) { - shm_init_ns(&init_ipc_ns); - return 0; + const int err = shm_init_ns(&init_ipc_ns); + WARN(err, "ipc: sysv shm_init_ns failed: %d\n", err); + return err; } pure_initcall(ipc_ns_init); -- cgit v1.1