netdev - Re: [RFC PATCH 1/2] net: use cmpxchg instead of spinlock in ptr rings

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Date:   Tue, 15 Nov 2016 16:30:57 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [RFC PATCH 1/2] net: use cmpxchg instead of spinlock in ptr rings

On Tue, Nov 15, 2016 at 02:32:58PM +0100, Jesper Dangaard Brouer wrote:
> What I would really like to see is a lock-free (locked cmpxchg) queue
> implementation, what like ptr_ring use the array as empty/full check,
> and still (somehow) support bulking.

I think lock-free is overrated for this use-case - we hold the lock
for such a short amount of time.

I think what we want is just a simpler spinlock - one that's faster than
qlock for use-cases that are unfair anyway, like this one where even if
you get the lock in a fair way, FIFO might be full and you won't be able
to queue.

Or find an API to add to FIFO in a fair way.

-- 
MST