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Date: Mon, 12 May 2014 11:19:52 -0700
From: Davidlohr Bueso <davidlohr@...com>
To: Manfred Spraul <manfred@...orfullife.com>
Cc: Davidlohr Bueso <davidlohr.bueso@...com>,
Michael Kerrisk <mtk.manpages@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, 1vier1@....de
Subject: Re: [PATCH 3/6] ipc/sem.c: remove code duplication
On Sat, 2014-05-10 at 12:03 +0200, Manfred Spraul wrote:
> count_semzcnt and count_semncnt are more of less identical.
> The patch creates a single function that either counts the number of tasks
> waiting for zero or waiting due to a decrease operation.
This is a nice cleanup.
> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
> ---
> ipc/sem.c | 103 ++++++++++++++++++++++++++++++--------------------------------
> 1 file changed, 50 insertions(+), 53 deletions(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index dc648f8..821aba7 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -47,8 +47,7 @@
> * Thus: Perfect SMP scaling between independent semaphore arrays.
> * If multiple semaphores in one array are used, then cache line
> * trashing on the semaphore array spinlock will limit the scaling.
> - * - semncnt and semzcnt are calculated on demand in count_semncnt() and
> - * count_semzcnt()
> + * - semncnt and semzcnt are calculated on demand in count_semcnt()
> * - the task that performs a successful semop() scans the list of all
> * sleeping tasks and completes any pending operations that can be fulfilled.
> * Semaphores are actively given to waiting tasks (necessary for FIFO).
> @@ -989,6 +988,31 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
> set_semotime(sma, sops);
> }
>
> +/*
> + * check_qop: Test how often a queued operation sleeps on the semaphore semnum
> + */
> +static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
> + bool count_zero)
Instead of directly calling check_qop(..., true/false), how about doing
something like the following? Should generate better code.
static inline int check_qop_zero(struct sem_array *sma, int semnum, struct sem_queue q)
{
return check_qop(sma, senum, q, true);
}
static linline int check_qop_nonzero(struct sem_array *sma, int semnum, struct sem_queue q)
{
return check_qop(sma, senum, q, false);
}
Perhaps instead of nonzero/zero we could replace it with the standard semncnt, semzcnt.
> +{
> + struct sembuf *sops = q->sops;
> + int nsops = q->nsops;
> + int i, semcnt;
> +
> + semcnt = 0;
> +
> + for (i = 0; i < nsops; i++) {
> + if (sops[i].sem_num != semnum)
> + continue;
> + if (sops[i].sem_flg & IPC_NOWAIT)
> + continue;
> + if (count_zero && sops[i].sem_op == 0)
> + semcnt++;
> + if (!count_zero && sops[i].sem_op < 0)
> + semcnt++;
> + }
> + return semcnt;
> +}
> +
> /* 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
> @@ -998,66 +1022,39 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
> * The counts we return here are a rough approximation, but still
> * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
> */
> -static int count_semncnt(struct sem_array *sma, ushort semnum)
> +static int count_semcnt(struct sem_array *sma, ushort semnum,
> + bool count_zero)
> {
> - int semncnt;
> + struct list_head *l;
> struct sem_queue *q;
> + int semcnt;
>
> - semncnt = 0;
nit: can we unify the declaration and assignment?
> - list_for_each_entry(q, &sma->sem_base[semnum].pending_alter, list) {
> - struct sembuf *sops = q->sops;
> - BUG_ON(sops->sem_num != semnum);
> - if ((sops->sem_op < 0) && !(sops->sem_flg & IPC_NOWAIT))
> - semncnt++;
> - }
> + semcnt = 0;
> + /* First: check the simple operations. They are easy to evaluate */
> + if (count_zero)
> + l = &sma->sem_base[semnum].pending_const;
> + else
> + l = &sma->sem_base[semnum].pending_alter;
>
> - list_for_each_entry(q, &sma->pending_alter, list) {
> + list_for_each_entry(q, l, list) {
> struct sembuf *sops = q->sops;
> - int nsops = q->nsops;
> - int i;
> - for (i = 0; i < nsops; i++)
> - if (sops[i].sem_num == semnum
> - && (sops[i].sem_op < 0)
> - && !(sops[i].sem_flg & IPC_NOWAIT))
> - semncnt++;
> - }
> - return semncnt;
> -}
>
> -static int count_semzcnt(struct sem_array *sma, ushort semnum)
> -{
> - int semzcnt;
> - struct sem_queue *q;
> -
> - semzcnt = 0;
> - list_for_each_entry(q, &sma->sem_base[semnum].pending_const, list) {
> - struct sembuf *sops = q->sops;
> BUG_ON(sops->sem_num != semnum);
> - if ((sops->sem_op == 0) && !(sops->sem_flg & IPC_NOWAIT))
> - semzcnt++;
> + BUG_ON(sops->sem_flg & IPC_NOWAIT);
> + BUG_ON(sops->sem_op > 0);
> + semcnt++;
> }
>
> - list_for_each_entry(q, &sma->pending_const, list) {
> - struct sembuf *sops = q->sops;
> - int nsops = q->nsops;
> - int i;
> - for (i = 0; i < nsops; i++)
> - if (sops[i].sem_num == semnum
> - && (sops[i].sem_op == 0)
> - && !(sops[i].sem_flg & IPC_NOWAIT))
> - semzcnt++;
> - }
> + /* Then: check the complex operations. */
> list_for_each_entry(q, &sma->pending_alter, list) {
> - struct sembuf *sops = q->sops;
> - int nsops = q->nsops;
> - int i;
> - for (i = 0; i < nsops; i++)
> - if (sops[i].sem_num == semnum
> - && (sops[i].sem_op == 0)
> - && !(sops[i].sem_flg & IPC_NOWAIT))
> - semzcnt++;
> + semcnt += check_qop(sma, semnum, q, count_zero);
> + }
> + if (count_zero) {
> + list_for_each_entry(q, &sma->pending_const, list) {
> + semcnt += check_qop(sma, semnum, q, count_zero);
> + }
> }
> - return semzcnt;
> + return semcnt;
> }
>
> /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
> @@ -1459,10 +1456,10 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
> err = curr->sempid;
> goto out_unlock;
> case GETNCNT:
> - err = count_semncnt(sma, semnum);
> + err = count_semcnt(sma, semnum, 0);
> goto out_unlock;
> case GETZCNT:
> - err = count_semzcnt(sma, semnum);
> + err = count_semcnt(sma, semnum, 1);
nit: use true/false in count_semcnt().
> goto out_unlock;
> }
>
Thanks,
Davidlohr
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