[PATCH 2/2] taskstats: use nla_reserve() for reply assembling

Oleg Nesterov
2006-11-01T18:27:50Z

Currently taskstats_user_cmd()/taskstats_exit() do:

1) allocate stats
2) fill stats
3) make a temporary copy on stack (236 bytes)
4) copy that copy to skb
5) free stats

With the help of nla_reserve() we can operate on skb->data directly,
thus avoiding all these steps except 2).

So, before this patch:

// copy *stats to skb->data
int mk_reply(skb, ..., struct taskstats *stats);

fill_pid(stats);
mk_reply(skb, ..., stats);

After:
// return a pointer to skb->data
struct taskstats *mk_reply(skb, ...);

stat = mk_reply(skb, ...);
fill_pid(stats);

Shrinks taskatsks.o by 162 bytes.

A stupid benchmark (send one million TASKSTATS_CMD_ATTR_PID) shows the
difference,

real user sys
before:
4.02 0.06 3.96
4.02 0.04 3.98
4.02 0.04 3.97
after:
3.86 0.08 3.78
3.88 0.10 3.77
3.89 0.09 3.80

but this looks suspiciously good.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

taskstats.c | 86 ++++++++++++++++++++++++++++++------------------------------
1 files changed, 44 insertions(+), 42 deletions(-)

--- STATS/kernel/taskstats.c~6_nla 2006-11-01 14:00:03.000000000 +0300
+++ STATS/kernel/taskstats.c 2006-11-01 21:14:39.000000000 +0300
@@ -190,6 +190,7 @@ static int fill_pid(pid_t pid, struct ta
} else
get_task_struct(tsk);

+ memset(stats, 0, sizeof(*stats));
/*
* Each accounting subsystem adds calls to its functions to
* fill in relevant parts of struct taskstsats as follows
@@ -232,6 +233,8 @@ static int fill_tgid(pid_t tgid, struct

if (first->signal->stats)
memcpy(stats, first->signal->stats, sizeof(*stats));
+ else
+ memset(stats, 0, sizeof(*stats));

tsk = first;
do {
@@ -348,9 +351,9 @@ static int parse(struct nlattr *na, cpum
return ret;
}

-static int mk_reply(struct sk_buff *skb, int type, u32 pid, struct taskstats *stats)
+static struct taskstats *mk_reply(struct sk_buff *skb, int type, u32 pid)
{
- struct nlattr *na;
+ struct nlattr *na, *ret;
int aggr;

aggr = TASKSTATS_TYPE_AGGR_TGID;
@@ -358,20 +361,23 @@ static int mk_reply(struct sk_buff *skb,
aggr = TASKSTATS_TYPE_AGGR_PID;

na = nla_nest_start(skb, aggr);
- NLA_PUT_U32(skb, type, pid);
- NLA_PUT_TYPE(skb, struct taskstats, TASKSTATS_TYPE_STATS, *stats);
+ if (nla_put(skb, type, sizeof(pid), &pid) < 0)
+ goto err;
+ ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats));
+ if (!ret)
+ goto err;
nla_nest_end(skb, na);

- return 0;
-nla_put_failure:
- return -1;
+ return nla_data(ret);
+err:
+ return NULL;
}

static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
{
int rc = 0;
struct sk_buff *rep_skb;
- struct taskstats stats;
+ struct taskstats *stats;
void *reply;
size_t size;
cpumask_t mask;
@@ -394,36 +400,36 @@ static int taskstats_user_cmd(struct sk_
size = nla_total_size(sizeof(u32)) +
nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);

- memset(&stats, 0, sizeof(stats));
rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, &reply, size);
if (rc < 0)
return rc;

+ rc = -EINVAL;
if (info->attrs[TASKSTATS_CMD_ATTR_PID]) {
u32 pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
- rc = fill_pid(pid, NULL, &stats);
- if (rc < 0)
- goto err;
+ stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid);
+ if (!stats)
+ goto nla_err;

- if (mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid, &stats))
- goto nla_put_failure;
+ rc = fill_pid(pid, NULL, stats);
+ if (rc < 0)
+ goto nla_err;
} else if (info->attrs[TASKSTATS_CMD_ATTR_TGID]) {
u32 tgid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_TGID]);
- rc = fill_tgid(tgid, NULL, &stats);
- if (rc < 0)
- goto err;
+ stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid);
+ if (!stats)
+ goto nla_err;

- if (mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid, &stats))
- goto nla_put_failure;
- } else {
- rc = -EINVAL;
+ rc = fill_tgid(tgid, NULL, stats);
+ if (rc < 0)
+ goto nla_err;
+ } else
goto err;
- }

return send_reply(rep_skb, info->snd_pid);

-nla_put_failure:
- rc = genlmsg_cancel(rep_skb, reply);
+nla_err:
+ genlmsg_cancel(rep_skb, reply);
err:
nlmsg_free(rep_skb);
return rc;
@@ -458,7 +464,7 @@ void taskstats_exit(struct task_struct *
{
int rc;
struct listener_list *listeners;
- struct taskstats *tidstats;
+ struct taskstats *stats;
struct sk_buff *rep_skb;
void *reply;
size_t size;
@@ -485,20 +491,17 @@ void taskstats_exit(struct task_struct *
if (list_empty(&listeners->list))
return;

- tidstats = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
- if (!tidstats)
- return;
-
rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, &reply, size);
if (rc < 0)
- goto free_stats;
+ return;

- rc = fill_pid(tsk->pid, tsk, tidstats);
- if (rc < 0)
- goto err_skb;
+ stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, tsk->pid);
+ if (!stats)
+ goto nla_err;

- if (mk_reply(rep_skb, TASKSTATS_TYPE_PID, tsk->pid, tidstats))
- goto nla_put_failure;
+ rc = fill_pid(tsk->pid, tsk, stats);
+ if (rc < 0)
+ goto nla_err;

/*
* Doesn't matter if tsk is the leader or the last group member leaving
@@ -506,20 +509,19 @@ void taskstats_exit(struct task_struct *
if (!is_thread_group || !group_dead)
goto send;

- if (mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tsk->tgid, tsk->signal->stats))
- goto nla_put_failure;
+ stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tsk->tgid);
+ if (!stats)
+ goto nla_err;
+
+ memcpy(stats, tsk->signal->stats, sizeof(*stats));

send:
send_cpu_listeners(rep_skb, listeners);
-free_stats:
- kmem_cache_free(taskstats_cache, tidstats);
return;

-nla_put_failure:
+nla_err:
genlmsg_cancel(rep_skb, reply);
-err_skb:
nlmsg_free(rep_skb);
- goto free_stats;
}

static struct genl_ops taskstats_ops = {