linux-kernel - Re: loaded router, excessive getnstimeofday in oprofile

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Message-ID: <21915755.1327801219904892242.JavaMail.root@ouachita>
Date:	Thu, 28 Aug 2008 02:28:12 -0400 (EDT)
From:	Joe Malicki <jmalicki@...acarta.com>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, johnpol@....mipt.ru, dada1@...mosbay.com,
	denys@...p.net.lb, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, juhlenko@...mai.com, sammy@...my.net
Subject: Re: loaded router, excessive getnstimeofday in oprofile

----- "David Miller" <davem@...emloft.net> wrote:
> 
> Every application using AF_PACKET sockets gets timestamps by
> default.  And we do know of several specific cases where the
> timestamps are unnecessary.
> 
> Even for other cases, why in the world does a DHCP client need
> accurate timestamps?  Give me a break. :)
> 

I've worked with systems where SO_TIMESTAMP has been used for
H.323 videoconferencing systems to synchronize audio and video
where remote systems' timestamps on the protocol streams proved
to be inaccurate (based off of different, unsynchronized clocks).

I can't see any other realistic use of this, but trying to get
timestamps for quasi-realtime protocols may be an important use
case - and in that case, you want the time when it hits the
interface, NOT when it hits the socket.

What utility does the time of hitting the socket get you?
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