From: Yang Yingliang <yangyingliang@huawei.com>
To: David Miller <davem@davemloft.net>
Cc: <netdev@vger.kernel.org>, <stephen@networkplumber.org>
Subject: Re: [PATCH net-next 4/4] sch_netem: replace spin_(un)lock_bh with sch_tree_(un)lock
Date: Fri, 14 Feb 2014 09:32:24 +0800 [thread overview]
Message-ID: <52FD7228.3010804@huawei.com> (raw)
In-Reply-To: <20140213.174606.334208738068503053.davem@davemloft.net>
On 2014/2/14 6:46, David Miller wrote:
> From: Yang Yingliang <yangyingliang@huawei.com>
> Date: Wed, 12 Feb 2014 10:58:15 +0800
>
>> spin_(un)lock_bh(root_lock) is same as sch_tree_(un)lock.
>>
>> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ...
>> @@ -684,11 +683,9 @@ static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr)
>> for (i = 0; i < n; i++)
>> d->table[i] = data[i];
>>
>> - root_lock = qdisc_root_sleeping_lock(sch);
>> -
>> - spin_lock_bh(root_lock);
>> + sch_tree_lock(sch);
>> swap(q->delay_dist, d);
>> - spin_unlock_bh(root_lock);
>> + sch_tree_unlock(sch);
>>
>> dist_free(d);
>> return 0;
>
> This is more expensive than the existing code.
>
> We will now calculate qdisc_root_sleeping_lock() twice which is at
> least two pointer dereferences each.
>
> Without explicitly open-coding this, the compiler cannot cache the
> result, because the spin lock operations have memory barriers (if
> implemented inline) or are considered to potentially modify all memory
> (if implemented as function calls).
>
>
OK, thanks!
I'll send v2 without this patch.
prev parent reply other threads:[~2014-02-14 1:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-12 2:58 [PATCH net-next 0/4] sch_netem: some improvements and cleanups Yang Yingliang
2014-02-12 2:58 ` [PATCH net-next 1/4] sch_netem: return errcode before setting params Yang Yingliang
2014-02-12 2:58 ` [PATCH net-next 2/4] sch_netem: change some func's param from "struct Qdisc *" to "struct netem_sched_data *" Yang Yingliang
2014-02-12 2:58 ` [PATCH net-next 3/4] sch_netem: replace magic numbers with enumerate in GE model Yang Yingliang
2014-02-12 2:58 ` [PATCH net-next 4/4] sch_netem: replace spin_(un)lock_bh with sch_tree_(un)lock Yang Yingliang
2014-02-13 22:46 ` David Miller
2014-02-14 1:32 ` Yang Yingliang [this message]
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