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From: Olivier Matz <olivier.matz@6wind.com>
To: Andrzej Ostruszka <amo@semihalf.com>
Cc: dev@dpdk.org, upstream@semihalf.com
Subject: Re: [PATCH 1/1] ring: fix off by 1 mistake
Date: Thu, 6 Jan 2022 11:45:21 +0100	[thread overview]
Message-ID: <YdbIQcplKPN6rz4q@platinum> (raw)
In-Reply-To: <20220103142201.475552-2-amo@semihalf.com>

Hi Andrzej,

On Mon, Jan 03, 2022 at 03:22:01PM +0100, Andrzej Ostruszka wrote:
> ring: fix off by 1 mistake

I suggest something less scary for the title:

  ring: optimize corner case for enqueue/dequeue

> When enqueueing/dequeueing to/from the ring we try to optimize by manual
> loop unrolling.  The check for this optimization looks like:
> 
> 	if (likely(idx + n < size)) {
> 
> where 'idx' points to the first usable element (empty slot for enqueue,
> data for dequeue).  The correct comparison here should be '<=' instead
> of '<'.
> 
> This is not a functional error since we fall back to the loop with
> correct checks on indexes.  Just a minor suboptimal behaviour for the
> case when we want to enqueue/dequeue exactly the number of elements that
> we have in the ring before wrapping to its beginning.
> 
> Signed-off-by: Andrzej Ostruszka <amo@semihalf.com>

Reviewed-by: Olivier Matz <olivier.matz@6wind.com>

I'll tend to add:
Fixes: cc4b218790f6 ("ring: support configurable element size")

But the same error was in the ENQUEUE_PTRS()/DEQUEUE_PTRS() macros
since the beginning, so we may also add:
Fixes: 286bd05bf70d ("ring: optimisations")

This macro was removed in commit 2d6ed071a8b9 ("ring: use custom element
for fixed size API")

Thanks!

next prev parent reply	other threads:[~2022-01-06 10:45 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-03 14:22 [PATCH 0/1] Minor mistake in ring (en|de)queueing Andrzej Ostruszka
2022-01-03 14:22 ` [PATCH 1/1] ring: fix off by 1 mistake Andrzej Ostruszka
2022-01-03 14:56   ` Morten Brørup
2022-01-06 10:45   ` Olivier Matz [this message]
2022-01-10 15:09   ` Ananyev, Konstantin
2022-01-11 11:49     ` Andrzej Ostruszka
2022-01-11 11:37   ` [PATCH] ring: optimize corner case for enqueue/dequeue Andrzej Ostruszka
2022-01-11 12:00     ` Morten Brørup
2022-01-11 13:46       ` Andrzej Ostruszka
2022-01-11 13:53         ` Morten Brørup
2022-02-05 16:48     ` David Marchand

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