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In order to speedup __inet_hash_connect(), we want to ensure hash values for <source address, port X, destination address, destination port> are not randomly spread, but monotonically increasing. Goal is to allow __inet_hash_connect() to derive the hash value of a candidate 4-tuple with a single addition in the following patch in the series. Given : hash_0 = inet_ehashfn(saddr, 0, daddr, dport) hash_sport = inet_ehashfn(saddr, sport, daddr, dport) Then (hash_sport == hash_0 + sport) for all sport values. As far as I know, there is no security implication with this change. After this patch, when __inet_hash_connect() has to try XXXX candidates, the hash table buckets are contiguous and packed, allowing a better use of cpu caches and hardware prefetchers. Tested: Server: ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog Client: ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog -c -H server Before this patch: utime_start=0.271607 utime_end=3.847111 stime_start=18.407684 stime_end=1997.485557 num_transactions=1350742 latency_min=0.014131929 latency_max=17.895073144 latency_mean=0.505675853 latency_stddev=2.125164772 num_samples=307884 throughput=139866.80 perf top on client: 56.86% [kernel] [k] __inet6_check_established 17.96% [kernel] [k] __inet_hash_connect 13.88% [kernel] [k] inet6_ehashfn 2.52% [kernel] [k] rcu_all_qs 2.01% [kernel] [k] __cond_resched 0.41% [kernel] [k] _raw_spin_lock After this patch: utime_start=0.286131 utime_end=4.378886 stime_start=11.952556 stime_end=1991.655533 num_transactions=1446830 latency_min=0.001061085 latency_max=12.075275028 latency_mean=0.376375302 latency_stddev=1.361969596 num_samples=306383 throughput=151866.56 perf top: 50.01% [kernel] [k] __inet6_check_established 20.65% [kernel] [k] __inet_hash_connect 15.81% [kernel] [k] inet6_ehashfn 2.92% [kernel] [k] rcu_all_qs 2.34% [kernel] [k] __cond_resched 0.50% [kernel] [k] _raw_spin_lock 0.34% [kernel] [k] sched_balance_trigger 0.24% [kernel] [k] queued_spin_lock_slowpath There is indeed an increase of throughput and reduction of latency. Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Tested-by: Jason Xing <kerneljasonxing@gmail.com> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com> Link: https://patch.msgid.link/20250305034550.879255-2-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.