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From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH] macvlan: lockless tx path
Date: Wed, 10 Nov 2010 22:12:35 +0100
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Cc: Ben Greear <greearb@candelatech.com>,
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To: Ben Hutchings <bhutchings@solarflare.com>
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Le mercredi 10 novembre 2010 =C3=A0 21:04 +0000, Ben Hutchings a =C3=A9=
crit :

> Drivers should calculate differences and accumulate them in a 64-bit
> counter.  (A lot of hardware has read-to-clear counters anyway, in wh=
ich
> 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.