Linux 3.5 Kernel Released

by moonboots • 14 years ago

192 36 14 years ago

A very nice networking feature has landed in 3.5: CODEL AQM packet scheduler to fight bufferbloat. It is mainly relevant for routers.

http://queue.acm.org/detail.cfm?id=2209336

Peaker4• 14 years ago

Some of the buffer bloat problem is due to SO_SENDBUF being statically set to some value, which also results in hiding the actual bytes-in-flight from the application.

I think it would be much better to allow the auto-detected TCP window to be exposed to the application level as the "send-buf" size (with perhaps some 10% buffer bloat to allow filling in the gaps when the window grows or acks return prematurely).

Also, it would be good for high-bandwidth-high-latency situations, where the default Linux 0.5MB send-buf size is not enough. Allow the send-buf to grow if the TCP window needs to grow beyond 0.5MB.

natermer2• 14 years ago

Well exposing it per application kinda defeats a bit of the purpose behind it. The point is that you get rid of the buffer so you get packet loss when the link to the other peer(s) is(are) saturated and allow the TCP congestion algorithms to work properly.

Even in a high latency high bandwidth situation having huge buffers is self-defeating. Anybody that has used Bittorrent and assumed their ISP was doing some sort of throttling were you have weird latency spikes and reduced performance... this is a direct result of buffer bloat in the majority of cases.

Large buffers only help in the case of a single TCP connection using up as much as the bandwidth as possible, which helps network routers and such things look good in benchmarks.

What you are talking about is some sort of Quality of Service type thing. Probably most usefully expressed at the edge of networks for prioritizing traffic and at the ISP level so they can route traffic through different internet links based on requirements.

ISPs have to deal with choosing different links to other networks and what it costs. They can do choose stuff like use main backbones versus secondary links and you get different trade-offs based cost versus latency and things of that nature. So ideally there should be some sort of flag you can set in the TCP packet that would indicate latency importance or some such thing. Or just making internet routing equipment application-protocol-aware.

noselasd3• 14 years ago

The socket send buffer from applications is not very relevant to buffer bloat, they do not cause retransmissions, nor do they contribute much visible latency.

dfc4• 14 years ago

I am looking forward to CODEL support in shorewall's simple or advanced traffic shaping scripts. I have tried to cobble together a custom `tcstart` file for CODEL and it has not been very successful. Does anyone have shorewall working with CODEL?

Also does anyone explain the difference between vanilla CODEL and FQ_CODEL? Is one an obvious choice over the other?

dfc4• 14 years ago

I have seen a number of people write that CODEL will be mainlined in 3.5. But from what I have seen it has been there for sometime now:

Initial CODEL commit entry from May:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git...

Search for CODEL in linus's tree:

http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Fl...

And there has not been a lot of CODEL activity in the net-next tree since the activity in May:

http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Fdavem%2Fnet-...

Am I missing something obvious?

harshreality• 14 years ago

Stable releases branch from Linus's tree. 3.4 branched on May 20th.

  git describe --contains 76e3cc126bb223013a6b9a0e2a51238d1ef2e409

esolyt• 14 years ago

It is worth nothing that Android is now closer to the mainline than ever. With this release, the kernel incorporates a functionality called autosleep which is similar to Android's wakelock, which was the main controversy between kernel developers and Google. Android team will now probably be able to switch to the new Linux infrastructure, if they wish so.

stingraycharles• 14 years ago

Here is a nice discussion on LWN about wakelock / autosleep: http://lwn.net/Articles/479841/

gnyman3• 14 years ago

Surely the Linux-kernel must by now be the worlds most advanced and most bloated kernel? Then again, the kernel is not the thousands of high quality modules (which I guess could be called drivers) which allow you access to the hardware.

Anybody know how the central kernel (the parts that are on all hardware) has evolved speed/size-wise?

Also, is the drivers in linux of higher quality than the ones for example windows? I have gotten the impression that it is so.

simcop2387• 14 years ago

As far as quality goes, it varies largely depending on the hardware. Some stuff is easy to figure out (or has specs published) and results in good quality stuff being available. Other things don't tend to fair so well, like the graphics drivers, and I believe many broadcom wifi adapters. However if you have something headless with a wired network you're generally not going to be able to ever be unhappy.

natermer2• 14 years ago

You get best bang for your buck by purchasing hardware that is made by companies that support Linux with open source drivers.

Example:

Purchasing random laptop off the internet that runs other OS because it is cool and then trying to install Linux on it is not going yield good results unless you are willing to spend a lot of time researching and making sure you bought something that will work well, as well as spend some time fiddling around with drivers a bit and filing a couple bug reports. This would be because your using hardware that no Linux developer has direct access too. Essentially you are the primary means of support for that particular OS/Hardware combination.

Or you can purchase laptop from a company that provides support for your particular Linux/hardware configuration (ie: they sell Linux pre-installed) and then you will likely get close to a 'Apple-like' experience with it 'just working' out of the box.

donky_cong• 14 years ago

Sadly this is untrue.

After working extensively with linux USB drivers by large corps like Philips, I cannot but assume they put their worst teams on the Linux drivers.

And as a proud owner of (what is widely considered the most supported linux laptop) lenovo laptop, I can say that many things just dont work. E.g. Suspend.

halayli2• 14 years ago

> most bloated kernel?

I wonder how you arrived to such conclusion.

gnyman3• 14 years ago

I was just thinking about how many new releases there have been and how little new things have actually affected me or the servers I administer in any way. Of course, most of the added stuff are not part of the core kernel and I will probably never run the code but still?

The thing that got me on this track was thinking about all the systems that still run the 2.6.X kernels (and maybe even 2.4.X), how much, if any improvements would they get from upgrading to 3.5?

rbanffy2• 14 years ago

> Also, is the drivers in linux of higher quality than the ones for example windows?

It really depends on the driver, but, at least, you can look into the code to see if it looks high quality. Or pay someone to do it.

Linux 3.5 Kernel Released

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