From: Stephen Hemminger <stephen@networkplumber.org>
To: "Morten Brørup" <mb@smartsharesystems.com>
Cc: dev@dpdk.org, "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
Subject: Re: [RFC] random: use per lcore state
Date: Mon, 11 Sep 2023 09:04:03 -0700 [thread overview]
Message-ID: <20230911090403.1c9afa42@fedora> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D87B7C@smartserver.smartshare.dk>
On Wed, 6 Sep 2023 19:54:32 +0200
Morten Brørup <mb@smartsharesystems.com> wrote:
> >
> > - idx = rte_lcore_id();
> > + seed = __atomic_load_n(&rte_rand_seed, __ATOMIC_RELAXED);
> > + if (unlikely(seed != rand_state->seed)) {
>
> Please note that rte_rand_seed lives in a completely different cache
> line than RTE_PER_LCORE(rte_rand_state), so the comparison with
> rte_rand_seed requires reading one more cache line than the original
> implementation, which only uses the cache line holding
> rand_states[idx].
>
> This is in the hot path.
>
> If we could register a per-thread INIT function, the lazy
> initialization could be avoided, and only one cache line accessed.
Since rte_rand_seed rarely changes, it will get cached by each cpu.
The problem was before there was prefetch cache overlap causing false
sharing.
next prev parent reply other threads:[~2023-09-11 16:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-06 17:20 Stephen Hemminger
2023-09-06 17:54 ` Morten Brørup
2023-09-11 16:04 ` Stephen Hemminger [this message]
2023-09-11 16:37 ` Morten Brørup
2023-09-06 18:16 ` Morten Brørup
2023-09-06 19:55 ` Stephen Hemminger
2023-09-06 20:12 ` Mattias Rönnblom
2023-09-06 20:02 ` Mattias Rönnblom
2023-09-06 23:00 ` Stephen Hemminger
2023-09-08 7:04 ` Mattias Rönnblom
2023-09-11 16:06 ` Stephen Hemminger
2023-09-11 16:53 ` Mattias Rönnblom
2023-09-09 0:13 ` Konstantin Ananyev
2023-09-09 6:45 ` Mattias Rönnblom
2023-09-09 11:23 ` Morten Brørup
2023-09-11 9:00 ` Mattias Rönnblom
2023-09-11 16:02 ` Stephen Hemminger
2023-09-09 11:32 ` Stephen Hemminger
2023-09-10 13:26 ` Konstantin Ananyev
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