netdev - Re: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

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Date:   Fri, 2 Feb 2018 18:44:02 +0800
From:   kbuild test robot <lkp@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     kbuild-all@...org, "Wong Hoi Sing, Edison" <hswong3i@...il.com>,
        "Hung Hing Lun, Mike" <hlhung3i@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

Hi Gustavo,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net/master]
[also build test ERROR on v4.15 next-20180202]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Gustavo-A-R-Silva/tcp_lp-use-64-bit-arithmetic-instead-of-32-bit/20180202-135349
config: i386-randconfig-i0-201804 (attached as .config)
compiler: gcc-7 (Debian 7.2.0-12) 7.2.1 20171025
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   net/ipv4/tcp_lp.o: In function `tcp_lp_remote_hz_estimator':
>> net/ipv4/tcp_lp.c:150: undefined reference to `__divdi3'

vim +150 net/ipv4/tcp_lp.c

   125	
   126	/**
   127	 * tcp_lp_remote_hz_estimator
   128	 *
   129	 * Estimate remote HZ.
   130	 * We keep on updating the estimated value, where original TCP-LP
   131	 * implementation only guest it for once and use forever.
   132	 */
   133	static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
   134	{
   135		struct tcp_sock *tp = tcp_sk(sk);
   136		struct lp *lp = inet_csk_ca(sk);
   137		s64 rhz = (s64)lp->remote_hz << 6;	/* remote HZ << 6 */
   138		s64 m = 0;
   139	
   140		/* not yet record reference time
   141		 * go away!! record it before come back!! */
   142		if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
   143			goto out;
   144	
   145		/* we can't calc remote HZ with no different!! */
   146		if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
   147		    tp->rx_opt.rcv_tsecr == lp->local_ref_time)
   148			goto out;
   149	
 > 150		m = (s64)TCP_TS_HZ *
   151		    (tp->rx_opt.rcv_tsval - lp->remote_ref_time) /
   152		    (tp->rx_opt.rcv_tsecr - lp->local_ref_time);
   153		if (m < 0)
   154			m = -m;
   155	
   156		if (rhz > 0) {
   157			m -= rhz >> 6;	/* m is now error in remote HZ est */
   158			rhz += m;	/* 63/64 old + 1/64 new */
   159		} else
   160			rhz = m << 6;
   161	
   162	 out:
   163		/* record time for successful remote HZ calc */
   164		if ((rhz >> 6) > 0)
   165			lp->flag |= LP_VALID_RHZ;
   166		else
   167			lp->flag &= ~LP_VALID_RHZ;
   168	
   169		/* record reference time stamp */
   170		lp->remote_ref_time = tp->rx_opt.rcv_tsval;
   171		lp->local_ref_time = tp->rx_opt.rcv_tsecr;
   172	
   173		return rhz >> 6;
   174	}
   175	

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