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authorManfred Spraul <manfred@colorfullife.com>2013-07-08 16:01:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-09 10:33:28 -0700
commitd12e1e50e47e0900dbbf52237b7e171f4f15ea1e (patch)
tree83b54585a883ee062353eb464d93944d08ab4a1c /ipc
parentf269f40ad5aeee229ed70044926f44318abe41ef (diff)
downloadlinux-d12e1e50e47e0900dbbf52237b7e171f4f15ea1e.tar.gz
ipc/sem.c: replace shared sem_otime with per-semaphore value
sem_otime contains the time of the last semaphore operation that completed successfully. Every operation updates this value, thus access from multiple cpus can cause thrashing. Therefore the patch replaces the variable with a per-semaphore variable. The per-array sem_otime is only calculated when required. No performance improvement on a single-socket i3 - only important for larger systems. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.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/sem.c37
1 files changed, 31 insertions, 6 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 6291257ee04..51352e1bfff 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -99,6 +99,7 @@ struct sem {
/* that alter the semaphore */
struct list_head pending_const; /* pending single-sop operations */
/* that do not alter the semaphore*/
+ time_t sem_otime; /* candidate for sem_otime */
} ____cacheline_aligned_in_smp;
/* One queue for each sleeping process in the system. */
@@ -911,8 +912,14 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
}
}
}
- if (otime)
- sma->sem_otime = get_seconds();
+ if (otime) {
+ if (sops == NULL) {
+ sma->sem_base[0].sem_otime = get_seconds();
+ } else {
+ sma->sem_base[sops[0].sem_num].sem_otime =
+ get_seconds();
+ }
+ }
}
@@ -1058,6 +1065,21 @@ static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in,
}
}
+static time_t get_semotime(struct sem_array *sma)
+{
+ int i;
+ time_t res;
+
+ res = sma->sem_base[0].sem_otime;
+ for (i = 1; i < sma->sem_nsems; i++) {
+ time_t to = sma->sem_base[i].sem_otime;
+
+ if (to > res)
+ res = to;
+ }
+ return res;
+}
+
static int semctl_nolock(struct ipc_namespace *ns, int semid,
int cmd, int version, void __user *p)
{
@@ -1131,9 +1153,9 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid,
goto out_unlock;
kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
- tbuf.sem_otime = sma->sem_otime;
- tbuf.sem_ctime = sma->sem_ctime;
- tbuf.sem_nsems = sma->sem_nsems;
+ tbuf.sem_otime = get_semotime(sma);
+ tbuf.sem_ctime = sma->sem_ctime;
+ tbuf.sem_nsems = sma->sem_nsems;
rcu_read_unlock();
if (copy_semid_to_user(p, &tbuf, version))
return -EFAULT;
@@ -2025,6 +2047,9 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
struct user_namespace *user_ns = seq_user_ns(s);
struct sem_array *sma = it;
+ time_t sem_otime;
+
+ sem_otime = get_semotime(sma);
return seq_printf(s,
"%10d %10d %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
@@ -2036,7 +2061,7 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
from_kgid_munged(user_ns, sma->sem_perm.gid),
from_kuid_munged(user_ns, sma->sem_perm.cuid),
from_kgid_munged(user_ns, sma->sem_perm.cgid),
- sma->sem_otime,
+ sem_otime,
sma->sem_ctime);
}
#endif