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Reworking 30 lines of Linux code could cut power use by up to 30 percent

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Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#31

Post by rvz »

> When I grew up in computer science in the 90s, everybody was concerned about efficiency...“Somehow in the last 20 years, this has gotten lost. Everybody’s completely gung-ho about performance without any regard for efficiency or resource consumption. I think it’s time to pivot, where we can find ways to make things a little more efficient.

This is the sort of performance efficiencies I want to keep seeing on this site, from those who are distinguished experts and contributed to critical systems such as the Linux kernel.

Unfortunately, in the last 10-15 years we are seeing the worst technologies being paraded due to a cargo-cultish behaviour. From asking candidates to implement the most efficient solution to a problem in interviews but then also choosing the most extremely inefficient technologies to solve certain problems because so-called software shops are racing for that VC money. Money that goes to hundreds of k8s instances on many over-provisioned servers instead of a few.

Performance efficiency critically matters, and it is the difference between having enough runway for a sustainable business vs having none at all.

And nope. AI Agents / Vibe coders could not have come up with a more correct solution in the article.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#32

Post by fnordpiglet »

ryao wrote: post #5

Linux added a busy polling feature for high performance networking. Most Linux software does not use it, but software used in datacenters (e.g. by CDNs) that does use it makes the system very energy inefficient when things are not busy. This patch gives the the kernel the ability to turn that off when not busy to regain energy efficiency until things become busy again. The article name is somewhat misleading, since i…

It’s a lot more nuanced than that. Being in a data center doesn’t imply heavy network utilization. The caveat is clearly outlined in the article being workload based not deployment based. If you have a home machine doing network routing it would absolutely benefit from this. In fact I would say probably the vast majority of Linux installs are home network devices, just people don’t know it. Embedded Linux machines doing network routing or switching or IPS or NAS or whatever would benefit a lot from this. “Energy savings” can be seen as a green washing statement but on embedded budgets it’s a primary requirement.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#33

Post by throw-qqqqq »

d3Xt3r wrote: post #2

> The code has been implemented as part of the Linux kernel release version 6.13 in January. This is basically 3 month old news now.

Well, I run Linux on both my laptops and desktops, consider myself an enthusiast etc., but I don’t track the development of the mainline Linux kernel closely enough to know what goes on there in the past three months.

I may notice changes when they get adopted by upstream maintainers of my distro, but that usually takes time..

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#34

Post by taeric »

fnordpiglet wrote: post #32
ryao wrote: post #5

Linux added a busy polling feature for high performance networking. Most Linux software does not use it, but software used in datacenters (e.g. by CDNs) that does use it makes the system very energy inefficient when things are not busy. This patch gives the the kernel the ability to turn that off when not busy to regain energy efficiency until things become busy again. The article name is somewhat misleading, since i…

It’s a lot more nuanced than that. Being in a data center doesn’t imply heavy network utilization. The caveat is clearly outlined in the article being workload based not deployment based. If you have a home machine doing network routing it would absolutely benefit from this. In fact I would say probably the vast majority of Linux installs are home network devices, just people don’t know it. Embedded Linux machines do…

I was curious how much this would be applicable to home routers.

I confess I'm dubious on major savings for most home users, though? At least, at an absolute level. 30% of less than five percent is still not that big of a deal. No reason not to do it, but don't expect to really see the results there.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#35

Post by fnordpiglet »

taeric wrote: post #34
fnordpiglet wrote: post #32

Earlier quoted context omitted.

It’s a lot more nuanced than that. Being in a data center doesn’t imply heavy network utilization. The caveat is clearly outlined in the article being workload based not deployment based. If you have a home machine doing network routing it would absolutely benefit from this. In fact I would say probably the vast majority of Linux installs are home network devices, just people don’t know it. Embedded Linux machines do…

I was curious how much this would be applicable to home routers. I confess I'm dubious on major savings for most home users, though? At least, at an absolute level. 30% of less than five percent is still not that big of a deal. No reason not to do it, but don't expect to really see the results there.

For embedded it’s not about saving cost it’s about saving limited on board power. The lower the power demand of the device, the smaller and the more you can dedicate to other things.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#36

Post by jeffbee »

fnordpiglet wrote: post #32
ryao wrote: post #5

Linux added a busy polling feature for high performance networking. Most Linux software does not use it, but software used in datacenters (e.g. by CDNs) that does use it makes the system very energy inefficient when things are not busy. This patch gives the the kernel the ability to turn that off when not busy to regain energy efficiency until things become busy again. The article name is somewhat misleading, since i…

It’s a lot more nuanced than that. Being in a data center doesn’t imply heavy network utilization. The caveat is clearly outlined in the article being workload based not deployment based. If you have a home machine doing network routing it would absolutely benefit from this. In fact I would say probably the vast majority of Linux installs are home network devices, just people don’t know it. Embedded Linux machines do…

What home router would be busy polling?

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#37

Post by taeric »

fnordpiglet wrote: post #35
taeric wrote: post #34

Earlier quoted context omitted.

I was curious how much this would be applicable to home routers. I confess I'm dubious on major savings for most home users, though? At least, at an absolute level. 30% of less than five percent is still not that big of a deal. No reason not to do it, but don't expect to really see the results there.

For embedded it’s not about saving cost it’s about saving limited on board power. The lower the power demand of the device, the smaller and the more you can dedicate to other things.

Again, no reason not to do this change. I'm not clear it helps in this case, though? The savings is in low use time. During high use time, it is the same, right?

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#38

Post by rvz »

queuebert wrote: post #7

This is really cool. As a high-performance computing professional, I've often wondered how much energy is wasted due to inefficient code and how much that is a problem as planetary compute scales up. For me, it feels like a moral imperative to make my code as efficient as possible, especially when a job will take months to run on hundreds of CPU.

Absolutely.

It is unfortunate that many software engineers continue to dismiss this as "premature optimization".

But as soon as I see resources or server costs gradually rising every month (even on idle usage) costing into the tens of thousands which is a common occurrence as the system scale, then it becomes unacceptable to ignore.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#39

Post by linsomniac »

Does this mean that "adaptive interrupt mitigation" is no longer a thing in the kernel? I haven't really messed with it in ~15+ years, but it used to be that the kernel would adapt, if network rate was low it would use interrupts, but then above a certain point it would switch to turning off interrupts and using polling instead.

The issue I was trying to resolve was sudden, dramatic changes in traffic. Think: a loop being introduced in the switching, and the associated packet storm. In that case, interrupts could start coming in so fast that the system couldn't get enough non-interrupted time to disable the interrupts, UNLESS you have more CPUs than busy networking interfaces. So my solution then was to make sure that the Linux routers had more cores than network interfaces.

Re: Reworking 30 lines of Linux code could cut power use by up to 30 percent

#40

Post by jeffbee »

toomuchtodo wrote: post #28
queuebert wrote: post #7

This is really cool. As a high-performance computing professional, I've often wondered how much energy is wasted due to inefficient code and how much that is a problem as planetary compute scales up. For me, it feels like a moral imperative to make my code as efficient as possible, especially when a job will take months to run on hundreds of CPU.

My experience with HPC is only tangential to being a sysadmin for data taking and cluster management for a high energy physics project; I am interested on your thoughts about using generative AI to search out for potentially power inefficient code paths in codebases for potential improvement.

Don't send an LLM to do a profiler's job.
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