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Differential D29522

tcp: For hostcache performance, use atomics instead of counters
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Authored by rscheff on Mar 31 2021, 10:29 PM.
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imp
melifaro

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Reviewers
jtl
tuexen
jhb
Group Reviewers
transport
Commits
rG254b56ac2a9e: tcp: For hostcache performance, use atomics instead of counters
rGe9ca38abc79b: tcp: For hostcache performance, use atomics instead of counters
rG4052275c2fc5: tcp: For hostcache performance, use atomics instead of counters
rG529a2a0f2765: tcp: For hostcache performance, use atomics instead of counters
Summary

As accessing the tcp hostcache happens frequently on some
classes of servers, it was recommended to use atomic_add/subtract
rather than (per-CPU distributed) counters, which have to be
summed up at high cost to cache efficiency.

This eliminates a counter_u64_fetch() from a hot path, introduced
by D29510.

PR: 254333
MFC after: 2 weeks
Sponsored by: NetApp, Inc.

Diff Detail

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rS FreeBSD src repository - subversion
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Buildable 38235
Build 35124: arc lint + arc unit

Event Timeline

rscheff created this revision.Mar 31 2021, 10:29 PM
Herald added 1 blocking reviewer(s): transport. · View Herald TranscriptMar 31 2021, 10:29 PM
Herald added subscribers: melifaro, imp. · View Herald Transcript
Harbormaster completed remote builds in B38228: Diff 86647.Mar 31 2021, 10:29 PM
rscheff requested review of this revision.Mar 31 2021, 10:29 PM
tuexen accepted this revision.Mar 31 2021, 10:50 PM
This revision is now accepted and ready to land.Mar 31 2021, 10:50 PM
jtl added a comment.Apr 1 2021, 1:11 AM

Thanks for doing this so quickly!

sys/netinet/tcp_hostcache.c
377

I think you need an atomic_load_int() here.

643–644

I think you need an atomic_load_int() here, although I don't think it functionally probably matters too much. In fact, this code already allows races between when the sysctl function is called to get the length, and when the code is called with another buffer. But, it seems like it is probably good to be consistent in using the atomic* functions to access or set atomic variables.

rscheff updated this revision to Diff 86657.Apr 1 2021, 7:19 AM
rscheff marked 2 inline comments as done.
  • use atomic access wrapper functions throughout
This revision now requires review to proceed.Apr 1 2021, 7:19 AM
Harbormaster completed remote builds in B38235: Diff 86657.Apr 1 2021, 7:19 AM
rscheff added a comment.Apr 1 2021, 7:20 AM

also did a line length wrap.

tuexen added inline comments.Apr 1 2021, 7:41 AM
sys/netinet/tcp_hostcache.c
644

Please put the operator at the end of the previous line.

655

Please put the operator at the end of the previous line.

rscheff updated this revision to Diff 86659.Apr 1 2021, 7:47 AM
  • move operator to end of line at wrap
Harbormaster completed remote builds in B38236: Diff 86659.Apr 1 2021, 7:47 AM
tuexen accepted this revision.Apr 1 2021, 7:51 AM
This revision is now accepted and ready to land.Apr 1 2021, 7:51 AM
Closed by commit rG529a2a0f2765: tcp: For hostcache performance, use atomics instead of counters (authored by rscheff). · Explain WhyApr 1 2021, 8:04 AM
This revision was automatically updated to reflect the committed changes.
rscheff added a commit: rG529a2a0f2765: tcp: For hostcache performance, use atomics instead of counters.
rscheff edited the summary of this revision. (Show Details)Apr 1 2021, 11:49 AM
rscheff added a commit: rG4052275c2fc5: tcp: For hostcache performance, use atomics instead of counters.Apr 16 2021, 8:46 PM
rscheff added a commit: rGe9ca38abc79b: tcp: For hostcache performance, use atomics instead of counters.Apr 16 2021, 9:34 PM
rscheff added a commit: rG254b56ac2a9e: tcp: For hostcache performance, use atomics instead of counters.Apr 16 2021, 10:12 PM

Revision Contents
Changeset List

PathSize
sys/
netinet/
2 lines
24 lines

Diff 86657

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sys/netinet/tcp_hostcache.h

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sys/netinet/tcp_hostcache.c

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