netdev - Re: [PATCH v2 net-next] tcp: switch rtt estimations to usec resolution

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Message-ID: <1393568072.26794.53.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 27 Feb 2014 22:14:32 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Julian Anastasov <ja@....bg>, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Larry Brakmo <brakmo@...gle.com>
Subject: Re: [PATCH v2 net-next] tcp: switch rtt estimations to usec
 resolution

On Thu, 2014-02-27 at 21:20 -0800, Andi Kleen wrote:
> Eric Dumazet <eric.dumazet@...il.com> writes:
> >  
> > -	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt, sack_rtt);
> > +	if (first_ackt.tv64) {
> > +		ktime_t curt = ktime_get_real();
> 
> Sorry I'm late to the party. One problem is that if a system doesn't use
> TSC for some reason this will be incredibly slow (unfortunately this
> happens for various reasons). Perhaps we need a
> ktime_get_real_but_use_jiffies_if_slow() or somesuch.

Right, so I cooked this instead :

http://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=363ec392352e55c61ce2799c3f15f89f9429bba7

Is this OK or do you see a problem with this ?

Thanks !


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