netdev - Re: [PATCH net-next 1/2] net: introduce generic net_random

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Message-ID: <1378210546.2048.20.camel@joe-AO722>
Date:	Tue, 03 Sep 2013 05:15:46 -0700
From:	Joe Perches <joe@...ches.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH net-next 1/2] net: introduce generic net_random_N helper

On Tue, 2013-09-03 at 13:40 +0200, Daniel Borkmann wrote:
> On 09/03/2013 01:00 PM, Joe Perches wrote:
> > On Tue, 2013-09-03 at 12:26 +0200, Daniel Borkmann wrote:
> >> We have implemented the same function over and over, so introduce a
> >> generic helper net_random_N() that unifies these implementations.
> >> It internally used net_random() which eventually resolves to
> >> prandom_u32(). Explicit include of reciprocal_div.h is not necessary.
> >
> > Perhaps adding a generic helper to random.h like
> > 	u32 prandom_u32_between(u32 low, u32 high);
> > or
> > 	u32 prandom_u32_range(u32 bound1, u32 bound2)
> > would be better.
> 
> Sure, this could be done as a follow-up. Once, we've migrated users to
> the new API, follow-ups could go ahead to do the rest, and migration
> will be easy. Note that the lower bound is 0 here.

Part of the reason I suggested this it to make the
API more readable/intelligible.

At first glance, I have no idea what net_random_N does.

I think #define net_random() prandom_u32()
should be removed eventually as well.

If gcc doesn't already do this optimization,
perhaps there are also some use of
	net_random() % non_const
that could be optimized a bit using this API.

$ git grep -E "(prandom_u32|net_random)\s*\(\s*\)\s*\%" net
net/batman-adv/bat_iv_ogm.c:	msecs += prandom_u32() % (2 * BATADV_JITTER);
net/batman-adv/bat_iv_ogm.c:	return jiffies + msecs_to_jiffies(prandom_u32() % (BATADV_JITTER / 2));
net/core/neighbour.c:	return base ? (net_random() % base) + (base >> 1) : 0;
net/core/neighbour.c:	unsigned long sched_next = now + (net_random() % p->proxy_delay);
net/core/pktgen.c:		flow = prandom_u32() % pkt_dev->cflows;
net/core/pktgen.c:			t = prandom_u32() %
net/core/pktgen.c:			mc = prandom_u32() % pkt_dev->src_mac_count;
net/core/pktgen.c:			mc = prandom_u32() % pkt_dev->dst_mac_count;
net/core/pktgen.c:			pkt_dev->cur_udp_src = prandom_u32() %
net/core/pktgen.c:			pkt_dev->cur_udp_dst = prandom_u32() %
net/core/pktgen.c:				t = prandom_u32() % (imx - imn) + imn;
net/core/pktgen.c:						t = prandom_u32() %
net/core/pktgen.c:			t = prandom_u32() %
net/core/stream.c:		current_timeo = vm_wait = (net_random() % (HZ / 5)) + 2;
net/ipv4/igmp.c:	int tv = net_random() % max_delay;
net/ipv4/igmp.c:	int tv = net_random() % in_dev->mr_maxdelay;
net/ipv4/igmp.c:	int tv = net_random() % delay;
net/ipv4/inet_connection_sock.c:		smallest_rover = rover = net_random() % remaining + low;
net/ipv6/addrconf.c:		rand_num = net_random() % (idev->cnf.rtr_solicit_delay ? : 1);
net/ipv6/mcast.c:	unsigned long tv = net_random() % idev->mc_maxdelay;
net/ipv6/mcast.c:	unsigned long tv = net_random() % delay;
net/ipv6/mcast.c:	unsigned long tv = net_random() % delay;
net/ipv6/mcast.c:			delay = net_random() % resptime;
net/ipv6/mcast.c:	delay = net_random() % unsolicited_report_interval(ma->idev);
net/netfilter/nf_conntrack_core.c:			(prandom_u32() % net->ct.sysctl_events_retry_timeout);
net/netfilter/nf_conntrack_core.c:		(prandom_u32() % net->ct.sysctl_events_retry_timeout);
net/sched/act_gact.c:	if (!gact->tcfg_pval || net_random() % gact->tcfg_pval)
net/sched/sch_netem.c:		skb->data[net_random() % skb_headlen(skb)] ^= 1<<(net_random() % 8);
net/sctp/socket.c:		rover = net_random() % remaining + low;
net/sunrpc/xprtsock.c:	unsigned short rand = (unsigned short) net_random() % range;
net/xfrm/xfrm_state.c:			spi = low + net_random()%(high-low+1);


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