Hi Jia,
Could you check if the patch below resolves the bug you have reported?
Just this patch, i.e. without your proposal.
I want to leave the optimization for the get_seconds() call:
We must update sem_otime in two places anyway
(either perform_atomic_semop() and exit_sem() or
do_smart_update() and semtimedop())
--
Manfred
In commit 0a2b9d4c,the update of semaphore's sem_otime(last semop time)
was moved to one central position (do_smart_update).
But: Since do_smart_update() is only called for operations that modify
the array, this means that wait-for-zero semops do not update sem_otime
anymore.
The fix is simple:
Non-alter operations must update sem_otime.
Signed-off-by: Manfred Spraul <[email protected]>
Reported-by: Jia He <[email protected]>
---
ipc/sem.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index e5d9bb8..ec83f79 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -910,6 +910,24 @@ again:
}
/**
+ * set_semotime(sma, sops) - set sem_otime
+ * @sma: semaphore array
+ * @sops: operations that modified the array, may be NULL
+ *
+ * sem_otime is replicated to avoid cache line trashing.
+ * This function sets one instance to the current time.
+ */
+static void set_semotime(struct sem_array *sma, struct sembuf *sops)
+{
+ if (sops == NULL) {
+ sma->sem_base[0].sem_otime = get_seconds();
+ } else {
+ sma->sem_base[sops[0].sem_num].sem_otime =
+ get_seconds();
+ }
+}
+
+/**
* do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
@@ -959,17 +977,10 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
}
}
}
- 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();
- }
- }
+ if (otime)
+ set_semotime(sma, sops);
}
-
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
@@ -1831,10 +1842,16 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = perform_atomic_semop(sma, sops, nsops, un,
task_tgid_vnr(current));
- if (error <= 0) {
- if (alter && error == 0)
+ if (error == 0) {
+ /* If the operation was successful, then do
+ * the required updates.
+ */
+ if (alter)
do_smart_update(sma, sops, nsops, 1, &tasks);
-
+ else
+ set_semotime(sma, sops);
+ }
+ if (error <= 0) {
goto out_unlock_free;
}
--
1.8.3.1
Tested-by: Jia He<[email protected]>
# cat /proc/sysvipc/sem
key semid perms nsems uid gid cuid cgid otime ctime
-1 32768 666 1 0 0 0 0 1380185570 1380185570
On Thu, 26 Sep 2013 07:08:55 +0200 from [email protected] wrote:
> Hi Jia,
>
> Could you check if the patch below resolves the bug you have reported?
> Just this patch, i.e. without your proposal.
>
> I want to leave the optimization for the get_seconds() call:
> We must update sem_otime in two places anyway
> (either perform_atomic_semop() and exit_sem() or
> do_smart_update() and semtimedop())
>
> --
> Manfred
>
> In commit 0a2b9d4c,the update of semaphore's sem_otime(last semop time)
> was moved to one central position (do_smart_update).
>
> But: Since do_smart_update() is only called for operations that modify
> the array, this means that wait-for-zero semops do not update sem_otime
> anymore.
>
> The fix is simple:
> Non-alter operations must update sem_otime.
>
> Signed-off-by: Manfred Spraul <[email protected]>
> Reported-by: Jia He <[email protected]>
> ---
> ipc/sem.c | 41 +++++++++++++++++++++++++++++------------
> 1 file changed, 29 insertions(+), 12 deletions(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index e5d9bb8..ec83f79 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -910,6 +910,24 @@ again:
> }
>
> /**
> + * set_semotime(sma, sops) - set sem_otime
> + * @sma: semaphore array
> + * @sops: operations that modified the array, may be NULL
> + *
> + * sem_otime is replicated to avoid cache line trashing.
> + * This function sets one instance to the current time.
> + */
> +static void set_semotime(struct sem_array *sma, struct sembuf *sops)
> +{
> + if (sops == NULL) {
> + sma->sem_base[0].sem_otime = get_seconds();
> + } else {
> + sma->sem_base[sops[0].sem_num].sem_otime =
> + get_seconds();
> + }
> +}
> +
> +/**
> * do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
> * @sma: semaphore array
> * @sops: operations that were performed
> @@ -959,17 +977,10 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
> }
> }
> }
> - 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();
> - }
> - }
> + if (otime)
> + set_semotime(sma, sops);
> }
>
> -
> /* The following counts are associated to each semaphore:
> * semncnt number of tasks waiting on semval being nonzero
> * semzcnt number of tasks waiting on semval being zero
> @@ -1831,10 +1842,16 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
>
> error = perform_atomic_semop(sma, sops, nsops, un,
> task_tgid_vnr(current));
> - if (error <= 0) {
> - if (alter && error == 0)
> + if (error == 0) {
> + /* If the operation was successful, then do
> + * the required updates.
> + */
> + if (alter)
> do_smart_update(sma, sops, nsops, 1, &tasks);
> -
> + else
> + set_semotime(sma, sops);
> + }
> + if (error <= 0) {
> goto out_unlock_free;
> }
>