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Old 10-01-2013, 06:20 AM   #1
BiloxiGeek
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Question Jumbo frames anyone?

Has anyone tried getting jumbo frames on their Roamio? Sometime in the next couple of days I'll have switches in my home network that all support jumbo frames. I run all my systems on static DHCP leases so I can send a jumbo frame sized MTU along with the lease. I just have no idea if the Roamio will use it or not.

I'm hoping to make my pyTivo transfers run a bit more efficiently if I can get the server and the Roamio talking with jumbo frames.
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Old 10-01-2013, 08:04 AM   #2
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I've never needed to use jumbo frames. For many years I've been able to get 900Mb/s+ speeds between devices on my network without using Jumbo Frames.
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Old 10-01-2013, 10:45 AM   #3
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There's no setting in the TiVo for jumbo frames, so you would have to hope that the NIC driver they use is able to handle them automatically.

In my experience, jumbo frames are almost always more trouble than they are worth as inevitably there is a device on the network that is interacting with the 'jumbo frame' devices that doesn't tolerate them particularly well (or at all).
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Old 10-01-2013, 11:18 AM   #4
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I'm hoping the network setup on the Roamio will take the MTU setting from DHCP. If it will, I can easily enable it on my pyTivo server and at least see what happens. As it stands each of my systems will be on a Gigabit connection except for the wireless mobile devices. I should be able to get everything else on jumbo frames pretty easily.

If nothing else it should be an interesting experiment assuming the Roamio will cooperate.
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Old 10-01-2013, 01:52 PM   #5
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It looks like the Roamio will run 1Gb/s and that interface should be capable of a 9000 MTU, however if all your devices on your segment do not have the same MTU value you will have problems, just ask the customer of mine I straightened out recently.

In reality you won't see any gain for internet traffic as ISPs only support 1500 byte packets (or less if you are still using PPPoE), you will potentially see an improvement when moving data around on your own local network, however the bottleneck tends to be the cheap consumer grade switches.

I'd suggest log a support call to TiVO although you might get a deer in the headlights response.

lastly I think its DHCP option #26 that you want, however if the TiVO doesn't use it it won't even request it.

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Old 10-01-2013, 01:59 PM   #6
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Well like you said, a call to TiVo support probably would only get the sound of crickets while the script monkeys try to google "Jumbo Frames". I figure if TiVo used a fairly standard dhclient it may just set the MTU correctly, have to wait till I get a new switch in the living room before I can test it. UPS has the switch out for delivery this afternoon.

If I can get a little better transfer rate from my linux/pyTivo server I'll be happy. If the jumbo frames start causing problems elsewhere on the home network I can always back off and go back to normal frame sizes.
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Old 10-01-2013, 03:10 PM   #7
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Just took a look at the posted source code for the TiVO and I'm not sure which version they are using as both 2.0 and 3.0.4 are included in the source tree. 2.0 although it should support MTU sizes may not do so reliably. version 3.0.4 should support setting the MTU size and I believe the default is to request the MTU parameter from the server.

What I don't know is exactly what TiVO modified if anything from the source code and I don't know what they used for the dhclient.conf file which can override the requested settings.

So your choices are
1) try it and see what happens
2) contact TiVO and see what they say

again don't forget EVERYTHING on your network MUST be set to the same MTU size or you will have problems. If you have any 100Mb/s ethernet devices you will have problems as they can't use jumbo frames.

I suspect your throughput will end up being either limited by the available CPU of the TiVO or the actual throughput of your switch, the gain for Jumbo frames will probably be minimal at best.

-TL
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Old 10-01-2013, 03:43 PM   #8
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The Roamio Pro already gets 190 mbps transfer rates.
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Old 10-01-2013, 03:51 PM   #9
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one thing that helps a lot more than Jumbo Frame is support for LSO (Large Segmentation Offload). This is assuming the Tivo's networking performance is CPU bound. Tivo network stack may already be using LSO (if not, their software engineers are more incompetent that I previously thought).

My observation on 10G and 40G Ethernet shows a -slight- improvement in CPU utilization using Jumbo frame -on receive side- (but I always have the LSO on. When LSO is on, the improvement on transmit side CPU utilization when using Jumbo Frames is not detectable). When running at line rate, the TCP payload throughput will -slightly- improve by using Jumbo Frames (slightly less per-packet overhead).

Tivo most of the time is transmitting. So I guess LSO support is more important than Jumbo Frame.
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Old 10-02-2013, 08:16 AM   #10
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Quote:
Originally Posted by aaronwt View Post
The Roamio Pro already gets 190 mbps transfer rates.
190Mb/s is roughly 20% of the theoretical maximum throughput which means the bottleneck would be the TiVO not the network. If you could hit 1Gb/s (1000Mb/s) the maximum throughput would be somewhere in the neighborhood of 120MBytes/s.

I highly doubt the TiVO is capable of that rate of throughput regardless of what the frame size is.
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Old 10-02-2013, 08:20 AM   #11
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Quote:
Originally Posted by Time_Lord View Post
190Mb/s is roughly 20% of the theoretical maximum throughput which means the bottleneck would be the TiVO not the network. If you could hit 1Gb/s (1000Mb/s) the maximum throughput would be somewhere in the neighborhood of 120MBytes/s.

I highly doubt the TiVO is capable of that rate of throughput regardless of what the frame size is.
Yes I know that. Without Jumbo frames I've been getting 900mbps+ speeds on my Network for many years. It was already known that the Roamio is not going to come anywhere close to gigabit speeds. But the transfer rates are much, much faster than any previous TiVo.
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Old 10-02-2013, 09:21 AM   #12
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Quote:
Originally Posted by Time_Lord View Post
Just took a look at the posted source code for the TiVO and I'm not sure which version they are using as both 2.0 and 3.0.4 are included in the source tree. 2.0 although it should support MTU sizes may not do so reliably. version 3.0.4 should support setting the MTU size and I believe the default is to request the MTU parameter from the server.

What I don't know is exactly what TiVO modified if anything from the source code and I don't know what they used for the dhclient.conf file which can override the requested settings.

So your choices are
1) try it and see what happens
2) contact TiVO and see what they say

again don't forget EVERYTHING on your network MUST be set to the same MTU size or you will have problems. If you have any 100Mb/s ethernet devices you will have problems as they can't use jumbo frames.

I suspect your throughput will end up being either limited by the available CPU of the TiVO or the actual throughput of your switch, the gain for Jumbo frames will probably be minimal at best.

-TL
FWIW: My Mini connects at 100BASE-TX.
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Old 10-02-2013, 11:27 AM   #13
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Quote:
Originally Posted by lew-wolfgang View Post
FWIW: My Mini connects at 100BASE-TX.
That's a good point that further de-legitimizes a Jumbo frame strategy for those who have Minis (at least Minis that are on ethernet and not MoCA)... the Mini does NOT have a 1000 interface. It is 100Mb only.
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