netdev - Re: [PATCH RFC] tcp: use seqlock for all cached tcp

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Message-ID: <alpine.LFD.2.00.1207222314230.2458@ja.ssi.bg>
Date:	Sun, 22 Jul 2012 23:34:38 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	David Miller <davem@...emloft.net>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH RFC] tcp: use seqlock for all cached tcp_metrics


	Hello,

On Sun, 22 Jul 2012, David Miller wrote:

> From: Julian Anastasov <ja@....bg>
> Date: Sun, 22 Jul 2012 12:44:28 +0300
> 
> > 	The ability to reclaim existing cache entries
> > requires metrics to be accessed with additional seqlock.
> > fastopen_cache tried to provide such locking for its values
> > but there is always the risk to access reclaimed entry.
> 
> I basically claim that accidental use of reclaimed entries
> is completely harmless for everything other than fastopen.
> 
> Therefore I do not advocate adding the new overhead and complexity for
> the non-fastopen cases.  It should be a completely free, lockless, and
> synchornization free cache.  If we read crap metrics, so be it, maybe
> the network dynamics changed to the same amount, and we would never
> know the different.  Therefore, it doesn't really matter if we read
> crap values for these measurements.

	OK, it seems I didn't understand you fully in previous
email. So, I can just send patch (or 2) for the tcpm_stamp and
tcp_tw_remember_stamp problems, now or after 2 weeks?

> Thanks.

Regards

--
Julian Anastasov <ja@....bg>
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