Date: Fri, 28 Sep 2001 14:34:39 -0400 From: "Louis A. Mamakos" <louie@TransSys.COM> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: tlambert2@mindspring.com, Jonathan Lemon <jlemon@flugsvamp.com>, the_srinivas@hotmail.com, hackers@FreeBSD.ORG Subject: timestamp offload [was Re: TCP&IP cksum offload on FreeBSD 4.2] Message-ID: <200109281834.f8SIYdZ77174@whizzo.transsys.com> In-Reply-To: Your message of "Fri, 28 Sep 2001 09:52:18 EDT." <15284.32914.874966.260722@grasshopper.cs.duke.edu> References: <200109270157.f8R1vZ546863@prism.flugsvamp.com> <3BB42E50.B32F5E95@mindspring.com> <15284.32914.874966.260722@grasshopper.cs.duke.edu>
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The cool thing I've always wanted to do with these programmable network adapters is to have them capture timestamps of when packets are received for high-accuracy latency measurements. The network adapter could drop a timestamp into some header when it's DMA'ed into the host's memory. The timestamp could come from some other PCI device (e.g., Datum bc635) which can provide a timestamp in 3 PCI bus cycles. The same sort of think could be done on transmit for suitably tagged packets. Some work I did a year or so ago measured the interrupt response time latency, and it was pretty impressive at how large and variable it could be. louie To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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