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SubjectRe: [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

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
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