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Date: Mon, 4 Aug 2014 21:52:27 -0700 From: Guy Harris <guy@...m.mit.edu> To: chetan loke <loke.chetan@...il.com> Cc: Daniel Borkmann <dborkman@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: Problems with TPACKET_V3 delivery of wakeups (and empty buffer blocks) On Aug 4, 2014, at 8:23 PM, chetan loke <loke.chetan@...il.com> wrote: > Empty buffer blocks have to be delivered. The patch explains it why. If by "the patch" you mean https://lkml.org/lkml/2011/6/21/463 and the comment > E2) Also implemented basic timeout mechanism to close 'a' current block. > That way, user-space won't be blocked forever on an idle link. > This is a much needed feature while monitoring multiple ports. > Look at 3) below. then that's presumably referring to 3.4.2 in > 3) Port aggregation analysis: > Multiple ports are viewed/analyzed as one logical pipe. > Example: > 3.1) up-stream path can be tapped in eth1 > 3.2) down-stream path can be tapped in eth2 > 3.3) Network TAP splits Rx/Tx paths and then feeds to eth1,eth2. > > If both eth1,eth2 need to be viewed as one logical channel, > then that implies we need to timesort the packets as they come across > eth1,eth2. > > 3.4) But following issues further complicates the problem: > 3.4.1)What if one stream is bursty and other is flowing > at line rate? > 3.4.2)How long do we wait before we can actually make a > decision in the app-space and bail-out from the spin-wait? and presumably this is referring to some mechanism by which eth1 and eth2 are handled by *one* socket, because if it's handled by *two* sockets, you use select()/poll()/epoll() on the two sockets, and, when *either* of the devices either fills up a block or times out, a wakeup is delivered to its socket and userland wakes up. And even if there's some reason why a wakeup has to be delivered when the timer expires even if *no* packets are available, what is the reason why you don't just deliver a wakeup but *no* buffer blocks, so that userland just says "well, I woke up, but there are no buffer blocks available for that particular socket, so there's nothing to process for that socket"?-- 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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