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From: "Lino Sanfilippo" <LinoSanfilippo@gmx.de>
To: "Eric Dumazet" <eric.dumazet@gmail.com>
Cc: "David Laight" <David.Laight@ACULAB.COM>,
	"David Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	"Tariq Toukan" <tariqt@mellanox.com>
Subject: Aw: Re: [PATCH] mlx4: give precise rx/tx bytes/packets counters
Date: Fri, 25 Nov 2016 17:30:57 +0100	[thread overview]
Message-ID: <trinity-a100658c-7fd5-47b3-ab3f-1f0a80774ccc-1480091457793@3capp-gmx-bs57> (raw)
In-Reply-To: <1480090590.8455.549.camel@edumazet-glaptop3.roam.corp.google.com>

Hi,


> 
> The READ_ONCE() are documenting the fact that no lock is taken to fetch
> the stats, while another cpus might being changing them.
> 
> I had no answer yet from https://patchwork.ozlabs.org/patch/698449/
> 
> So I thought it was not needed to explain this in the changelog, given
> that it apparently is one of the few things that can block someone to
> understand one of my changes :/
> 
> Apparently nobody really understands READ_ONCE() purpose, it is really a
> pity we have to explain this over and over.
> 

Even at the risk of showing once more a lack of understanding for READ_ONCE():
Does not a READ_ONCE() have to e paired with some kind of WRITE_ONCE()? 
Furthermore: there a quite some network drivers that ensure visibility of 
the descriptor queue indices between xmit and xmit completion function by means of
smp barriers. Could all these drivers theoretically be adjusted to use READ_ONCE(),
WRITE_ONCE() for the indices instead?

Regards,
Lino

  reply	other threads:[~2016-11-25 16:31 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-25 15:46 [PATCH] mlx4: give precise rx/tx bytes/packets counters Eric Dumazet
2016-11-25 16:03 ` David Laight
2016-11-25 16:16   ` Eric Dumazet
2016-11-25 16:30     ` Lino Sanfilippo [this message]
2016-11-25 19:19       ` Aw: " Eric Dumazet
2016-11-28 22:02         ` Lino Sanfilippo
2016-11-29  0:19           ` Eric Dumazet
2016-11-30 15:28             ` David Laight
2016-11-30 15:47               ` Eric Dumazet
2016-11-26 22:47 ` Saeed Mahameed
2016-11-27  2:16   ` Eric Dumazet
2016-11-28 20:40     ` David Miller
2016-11-28 21:55       ` Saeed Mahameed
2016-11-28 22:57         ` Eric Dumazet
2016-11-29 18:37 ` David Miller
2016-11-30 14:08 ` Regression: " Jesper Dangaard Brouer
2016-11-30 15:58   ` Eric Dumazet
2016-11-30 16:46     ` Saeed Mahameed
2016-11-30 17:35       ` Eric Dumazet
2016-11-30 20:42         ` Saeed Mahameed
2016-11-30 21:00           ` Eric Dumazet
2016-12-01 12:37             ` Jesper Dangaard Brouer
2016-12-01 13:02               ` [PATCH net-next] mlx4: fix use-after-free in mlx4_en_fold_software_stats() Eric Dumazet
2016-12-01 15:23                 ` Saeed Mahameed
2016-12-02 18:36                 ` David Miller
2016-12-01 15:38             ` Regression: [PATCH] mlx4: give precise rx/tx bytes/packets counters Saeed Mahameed
2016-12-01 15:55               ` Eric Dumazet
2016-12-01 16:08                 ` Eric Dumazet
2016-12-01 17:36                   ` Eric Dumazet
2016-12-04 13:23                     ` Saeed Mahameed
2016-12-01 16:33                 ` Saeed Mahameed
2016-12-01 17:08                   ` Eric Dumazet
2016-12-04 13:21                     ` Saeed Mahameed

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