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Message-ID: <20080827183216.GZ26610@one.firstfloor.org> Date: Wed, 27 Aug 2008 20:32:16 +0200 From: Andi Kleen <andi@...stfloor.org> To: Eric Dumazet <dada1@...mosbay.com> Cc: Andi Kleen <andi@...stfloor.org>, Rick Jones <rick.jones2@...com>, Evgeniy Polyakov <johnpol@....mipt.ru>, Denys Fedoryshchenko <denys@...p.net.lb>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: loaded router, excessive getnstimeofday in oprofile\ > Doing the expensive timestamping in a possibly delayed thread (ie some > milliseconds > after hardware notification) is wrong/useless. We had this discussion earlier, please review the thread I linked to. Note that interrupts can be arbitarily delayed too (both by cli and by interrupt mitigation), even on a non RT kernel. If you want exact notification (packet arriving at your NIC's buffers) you need NIC hardware support (and more and more NICs have it[1]). If you do it in software then even the interrupt is at the end of a long queue with a pretty much arbitary delay. Doing it in socket context is just one queue more. It's pretty much all arbitary. The argument for doing it as late as possible is the prohibitive cost on some systems as people notice all the time. -Andi [1] Unfortunately not necessarily synchronized with system time. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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