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Cause: In order to optimize network traffic and avoid sending partial LDAP responses, 389-ds uses TCP_CORK socket option. This socket option is useless because LDAP server always send complete responses/results
Consequence: To use TCP_CORK, LDAP server does setsockopt syscall per resp/result. But the use of TCP_CORK is useless in case of 389-ds
Fix: set nagle=off by default
Result: reduce the number of setsockopt calls
Description of problem:
nagle is enabled by default. To prevent returned search entries/result to be stuck the server set/reset (setsocketopt) TCP_CORK. It can give a network benefit in term of transmitted overhead, but the cost is a big use of systemcall setsocketopt.
The benefit of nagle should be limited by the fact that DS always write complete PDU (response or entries)
Switching on/off nagle has no significant impact on throughput but gives benefit in terms of syscall
tracing: perf trace -t <worker> -s
NAGLE: off
ns-slapd (108026), 1527476 events, 100.0%
syscall calls total min avg max stddev
(msec) (msec) (msec) (msec) (%)
--------------- -------- --------- --------- --------- --------- ------
futex 328122 3059.967 0.000 0.009 360.607 19.06%
poll 124478 854.697 0.002 0.007 100.142 20.29%
sendto 124149 785.173 0.002 0.006 0.041 0.11%
write 123627 483.753 0.002 0.004 0.080 0.10%
recvfrom 62295 245.209 0.002 0.004 0.040 0.12%
madvise 9 0.211 0.016 0.023 0.042 12.46%
sched_yield 34 0.146 0.004 0.004 0.005 1.32%
NAGLE: on
ns-slapd (108026), 1784094 events, 100.0%
syscall calls total min avg max stddev
(msec) (msec) (msec) (msec) (%)
--------------- -------- --------- --------- --------- --------- ------
futex 328704 3054.546 0.000 0.009 346.687 17.23%
setsockopt 124702 656.760 0.001 0.005 0.034 0.14%
poll 125437 655.709 0.002 0.005 100.141 15.28%
sendto 124501 464.307 0.001 0.004 0.039 0.14%
write 125026 462.438 0.001 0.004 0.031 0.10%
recvfrom 62799 248.383 0.002 0.004 0.030 0.11%
madvise 3 0.066 0.014 0.022 0.034 26.97%
sched_yield 10 0.043 0.004 0.004 0.004 1.69%
Version-Release number of selected component (if applicable):
How reproducible:
Will be described later
Actual results:
With searchrate, we can see as much setsockopt than the #write
Expected results:
See lower number of setsockopt
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (389-ds:1.4 bug fix and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2021:1835
Description of problem: nagle is enabled by default. To prevent returned search entries/result to be stuck the server set/reset (setsocketopt) TCP_CORK. It can give a network benefit in term of transmitted overhead, but the cost is a big use of systemcall setsocketopt. The benefit of nagle should be limited by the fact that DS always write complete PDU (response or entries) Switching on/off nagle has no significant impact on throughput but gives benefit in terms of syscall tracing: perf trace -t <worker> -s NAGLE: off ns-slapd (108026), 1527476 events, 100.0% syscall calls total min avg max stddev (msec) (msec) (msec) (msec) (%) --------------- -------- --------- --------- --------- --------- ------ futex 328122 3059.967 0.000 0.009 360.607 19.06% poll 124478 854.697 0.002 0.007 100.142 20.29% sendto 124149 785.173 0.002 0.006 0.041 0.11% write 123627 483.753 0.002 0.004 0.080 0.10% recvfrom 62295 245.209 0.002 0.004 0.040 0.12% madvise 9 0.211 0.016 0.023 0.042 12.46% sched_yield 34 0.146 0.004 0.004 0.005 1.32% NAGLE: on ns-slapd (108026), 1784094 events, 100.0% syscall calls total min avg max stddev (msec) (msec) (msec) (msec) (%) --------------- -------- --------- --------- --------- --------- ------ futex 328704 3054.546 0.000 0.009 346.687 17.23% setsockopt 124702 656.760 0.001 0.005 0.034 0.14% poll 125437 655.709 0.002 0.005 100.141 15.28% sendto 124501 464.307 0.001 0.004 0.039 0.14% write 125026 462.438 0.001 0.004 0.031 0.10% recvfrom 62799 248.383 0.002 0.004 0.030 0.11% madvise 3 0.066 0.014 0.022 0.034 26.97% sched_yield 10 0.043 0.004 0.004 0.004 1.69% Version-Release number of selected component (if applicable): How reproducible: Will be described later Actual results: With searchrate, we can see as much setsockopt than the #write Expected results: See lower number of setsockopt