netdev - Re: [RFC v3 3/6] can: make struct proto const

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Message-ID: <20110315221253.GA380@e-circ.dyndns.org>
Date:	Tue, 15 Mar 2011 23:12:53 +0100
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	socketcan-core@...ts.berlios.de, netdev@...r.kernel.org
Subject: Re: [RFC v3 3/6] can: make struct proto const

On Tue, Mar 15, 2011 at 10:28:13PM +0100, Oliver Hartkopp wrote:
> On 14.03.2011 18:17, Kurt Van Dijck wrote:
> > On Mon, Mar 14, 2011 at 05:42:23PM +0100, Eric Dumazet wrote:
> >> Le lundi 14 mars 2011 à 16:02 +0100, Kurt Van Dijck a écrit :
> >>
> >>> I see your point.
> >>> The reason I modified this was, as described, checkpatch.pl was complaining.
> >>> Anyway, this sequence was protected by a spinlock 'proto_tab_lock'.
> >>> I don't think it was a race.
> >>>
> >>> Did I miss something?
> >>
> >> As soon as proto_tab[proto] = cp; is done, another thread on another cpu
> >> can read the pointer and follow it.
> >>
> >> Hmm, I missed can_create() also uses the spinlock protection, so you're
> >> probably right.
> >>
> >> It seems a bit overkill :(
> >> phonet uses RCU for example.
> 
> Hello Eric,
> 
> the RCU code in phonet is worth to consider. But loading and removing of
> protocols is far away from being a hot path ... what would be the advantages
> to move to RCU here?
Does RCU avoid a spinlock?

> 
> > I'll keep that in mind.
> > Switching CAN protos to RCU is far beyond to goal of this patch :-)
> 
> Anyway making the struct proto a const (and set the default defines in the CAN
> protocols) is a nice cleanup. Let's wait for the feedback about the RCU from
> Eric ... then this patch could be put into mainline independently from the
> j1939 protocol.
ack.

Kurt
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