From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: christoph.paasch@uclouvain.be, netdev@vger.kernel.org
Subject: Re: [RFC net] tcp: metrics: Avoid duplicate entries with the same destination-IP
Date: Wed, 15 Jan 2014 12:18:56 -0800 (PST) [thread overview]
Message-ID: <20140115.121856.712581760900022040.davem@davemloft.net> (raw)
In-Reply-To: <1389631669.31367.221.camel@edumazet-glaptop2.roam.corp.google.com>
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 13 Jan 2014 08:47:49 -0800
> On Mon, 2014-01-13 at 16:25 +0100, Christoph Paasch wrote:
>
>> Another solution might be to leave tcp_get_metrics() as it is, and in
>> tcpm_new do another call to __tcp_get_metrics() while holding the
>> spin-lock. We would then check __tcp_get_metrics twice for new entries
>> but we won't hold the spin-lock needlessly anymore.
>
> This is the only solution if you want to fix this.
> Cost of lookup are the cache line misses.
> Avoiding the spinlock is a must.
>
> The second 'lookup' is basically free, as the first one have populated
> cpu caches.
Indeed, taking the lock in tcp_get_metrics() is to be avoided at all
costs.
next prev parent reply other threads:[~2014-01-15 20:18 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-13 15:25 [RFC net] tcp: metrics: Avoid duplicate entries with the same destination-IP Christoph Paasch
2014-01-13 16:47 ` Eric Dumazet
2014-01-15 20:18 ` David Miller [this message]
2014-01-15 23:21 ` Christoph Paasch
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