netdev - Re: [PATCH] macvlan: lockless tx path

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Date:	Wed, 10 Nov 2010 22:12:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] macvlan: lockless tx path

Le mercredi 10 novembre 2010 à 21:04 +0000, Ben Hutchings a écrit :

> Drivers should calculate differences and accumulate them in a 64-bit
> counter.  (A lot of hardware has read-to-clear counters anyway, in which
> case the driver *has* to accumulate the values it reads.)

You are mistaken. These are _hardware_ counters. If they were software,
of course they would be 32 or 64 bit.

And doing the thing you describe in software is racy.
I tried to remove many races, not to add new ones.

Yes, some drivers read one hardware counter using two instructions, and
this is racy.



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