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Message-Id: <20140213.174606.334208738068503053.davem@davemloft.net> Date: Thu, 13 Feb 2014 17:46:06 -0500 (EST) From: David Miller <davem@...emloft.net> To: yangyingliang@...wei.com Cc: netdev@...r.kernel.org, stephen@...workplumber.org Subject: Re: [PATCH net-next 4/4] sch_netem: replace spin_(un)lock_bh with sch_tree_(un)lock From: Yang Yingliang <yangyingliang@...wei.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@...wei.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). -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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