From: 王志强 <00107082@163.com>
To: musl@lists.openwall.com
Subject: [musl] on aarch64, dns A/AAAA queries has high probability of having same dns transaction ID, causing 5s delay
Date: Tue, 5 Jan 2021 21:44:32 +0800 (CST) [thread overview]
Message-ID: <8884803.698a.176d2cac33c.Coremail.00107082@163.com> (raw)
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Hi guys,
I am having lots of dns 5s delay on a arm/aarch64 platform, after tcpdump capturing dns packages, I found that the delay always happened when A/AAAA queries happened to have same dns transaction id.
network/res_mkquery.c
...
/* Make a reasonably unpredictable id */
clock_gettime(CLOCK_REALTIME, &ts);
id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;
q[0] = id/256;
q[1] = id;
...
time/clock_gettime.c
...
r = __syscall(SYS_clock_gettime, clk, ts);
if (r == -ENOSYS) {
if (clk == CLOCK_REALTIME) {
__syscall(SYS_gettimeofday, ts, 0);
ts->tv_nsec = (int)ts->tv_nsec * 1000;
return 0;
}
r = -EINVAL;
}
return __syscall_ret(r);
....
On aarch64, gettimeofday yields current time with low accuracy, the smallest unit is 1e-6, (I think)
Could we add some trick to make sure that the parallel A/AAAA queries got different id?
Thanks
David
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next reply other threads:[~2021-01-05 13:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 13:44 王志强 [this message]
2021-01-07 1:38 ` [musl] " 王志强
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