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From: Stephen Hemminger <stephen@networkplumber.org>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>
Cc: dev@dpdk.org, "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
	"Morten Brørup" <mb@smartsharesystems.com>
Subject: Re: [RFC] random: use per lcore state
Date: Wed, 6 Sep 2023 16:00:04 -0700	[thread overview]
Message-ID: <20230906160004.333b0488@hermes.local> (raw)
In-Reply-To: <c661fdd6-ada8-b94e-d01b-b5394eed5d84@lysator.liu.se>

On Wed, 6 Sep 2023 22:02:54 +0200
Mattias Rönnblom <hofors@lysator.liu.se> wrote:

> On 2023-09-06 19:20, Stephen Hemminger wrote:
> > Move the random number state into thread local storage.  
> 
> Me and Morten discussed TLS versus other alternatives in some other 
> thread. The downside of TLS that Morten pointed out, from what I recall, 
> is that lazy initialization is *required* (since the number of threads 
> is open-ended), and the data ends up in non-huge page memory. It was 
> also unclear to me what the memory footprint implications would be, 
> would large per-lcore data structures be put in TLS. More specifically, 
> if they would be duplicated across all threads, even non-lcore threads.

But current method is unsafe on non-lcore threads.
Two non-lcore threads calling rte_rand() will clash on state without
any locking protection.

Also, right now the array is sized at 129 entries to allow for the
maximum number of lcores. When the maximum is increased to 512 or 1024
the problem will get worse.

  reply	other threads:[~2023-09-06 23:00 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
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 [this message]
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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