netdev - Re: [PATCH net-next v3 1/2] net: sched: add empty status flag for NOLOCK qdisc

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Message-ID: <ad34151a-308e-ed16-32c0-8f99f6db24e3@gmail.com>
Date:   Fri, 22 Mar 2019 08:18:02 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Ivan Vecera <ivecera@...hat.com>
Subject: Re: [PATCH net-next v3 1/2] net: sched: add empty status flag for
 NOLOCK qdisc



On 03/22/2019 08:01 AM, Paolo Abeni wrote:
> The queue is marked not empty after acquiring the seqlock,
> and it's up to the NOLOCK qdisc clearing such flag on dequeue.
> Since the empty status lays on the same cache-line of the
> seqlock, it's always hot on cache during the updates.
> 
> This makes the empty flag update a little bit loosy. Given
> the lack of synchronization between enqueue and dequeue, this
> is unavoidable.
> 

Reviewed-by: Eric Dumazet <edumazet@...gle.com>