So an exokernel?
People don't use actual exokernels; they just use Linux like an exokernel. Aka "1975 programming".
The C10M problem
31–40 of 116 posts
Re: The C10M problem
#32Earlier quoted context omitted.
The entire purpose is to NOT route stuff through the kernel. TFA explains how to do it, and I've done it myself. You can set a flag on the Linux kernel when it boots limiting it to the first N cores. I usually use 2. The remaining cores are completely idle—Linux will not schedule any threads on those cores. Then you build an app that works more-or-less like Snabb Switch, which talks directly to the Ethernet adaptor,…
Linux will often still schedule kernel threads to run on those cores so they are not totally isolated. Also cache effects. If your architecture shares caches between cores, sometimes it would be worth "wasting" a neighboring core to avoid ssh and gdb thrashing your cache. Oh and also don't forget to set up IRQ affinity to avoid any of those cores to handle. There is an interesting research done by Siemens, that takes…
> Linux will often still schedule kernel threads to run on those cores so they are not totally isolated.
Have a look at cpuset[0]. You can forcibly move kernel threads into a given set (even pinned threads), and then force that set onto whatever cores you want.
[0] http://www.kernel.org/doc/man-pages/online/pages/man7/cpuset...
Re: The C10M problem
#33On the one hand, I love this. There's an old-school, down-to-the-metal, efficiency-is-everything angle that resonates deeply with me. On the other hand, I worry that just means I'm old. There are a lot of perfectly competent developers out there that have very little idea about the concerns that motivate thinking like this C10M manifesto. I sometimes wonder if my urge toward efficiency something like my grandmother's…
I believe it's what used to be called 'craftsmanship'. Taking pride in creating things that are efficient and not wasteful for no other reason than the desire to make the best product possible.
A beautifully carved chair may display excellent craftsmanship, but if you spend three months carving the world's most beautiful chair when the client asked for a dozen basic ladderbacks for a dinner party next Friday, you're not a very wise craftsman.
Similarly, if your software runs in 1% of CPU on a typical customer's machine, spending 10x the time and resources to make it run in 0.1% is not laudable. Context is everything.
Re: The C10M problem
#34On the one hand, I love this. There's an old-school, down-to-the-metal, efficiency-is-everything angle that resonates deeply with me. On the other hand, I worry that just means I'm old. There are a lot of perfectly competent developers out there that have very little idea about the concerns that motivate thinking like this C10M manifesto. I sometimes wonder if my urge toward efficiency something like my grandmother's…
I believe it's what used to be called 'craftsmanship'. Taking pride in creating things that are efficient and not wasteful for no other reason than the desire to make the best product possible.
It is wasteful to spend time doing something that benefits nobody, or where the benefits outweigh the cost. Your time is worth something.
Re: The C10M problem
#35On the one hand, I love this. There's an old-school, down-to-the-metal, efficiency-is-everything angle that resonates deeply with me. On the other hand, I worry that just means I'm old. There are a lot of perfectly competent developers out there that have very little idea about the concerns that motivate thinking like this C10M manifesto. I sometimes wonder if my urge toward efficiency something like my grandmother's…
Not at all. I think that it's our perspective shifted, because our every day computers became so fast, with more CPU and more RAM, that the average programmer doesn't feel the pain of inefficient code anymore.
I've seen enough software that is "very fast and scalable", because it wasn't tested at really large deployments.
Of course, that's not always what your software needs or wants, but in the case of internet backend software and hardware, it's a huge difference if your servers have 1, 10 or 100 times the throughput.
Also, many developers are client developers where this is a not the problem it used to be. In 1990, when a game didn't fit into a few kB of memory or didn't ran fast enough, the developer assembler-optimized the hell out of it, today most of this doesn't matter except for the software everyone uses but noone writes (your ISPs webmail, dropbox, twitter and whatever internet site has enough users).
Re: The C10M problem
#36Earlier quoted context omitted.
I believe it's what used to be called 'craftsmanship'. Taking pride in creating things that are efficient and not wasteful for no other reason than the desire to make the best product possible.
It is wasteful to spend time doing something that benefits nobody, or where the benefits outweigh the cost. Your time is worth something.
The point I was trying to make is that if you spend your time to make something that works really efficiently, and you take pride in it, then you haven't wasted your time. It doesn't benefit nobody, it benefits yourself, because you can take pride in your work. At least, I believe this idea is part of what's implied in the traditional notion of 'craftsmanship'.
An example might be working nine hours per day rather than eight to produce something that only uses 10% of the resources (and that extra hour is unpaid). For some people, that extra hour would be a waste, but for others, it would bring them greater satisfaction knowing they'd delivered a more efficient product, even if it brought them no extra revenue.
Re: The C10M problem
#37Earlier quoted context omitted.
Linux will often still schedule kernel threads to run on those cores so they are not totally isolated. Also cache effects. If your architecture shares caches between cores, sometimes it would be worth "wasting" a neighboring core to avoid ssh and gdb thrashing your cache. Oh and also don't forget to set up IRQ affinity to avoid any of those cores to handle. There is an interesting research done by Siemens, that takes…
> Linux will often still schedule kernel threads to run on those cores so they are not totally isolated. Have a look at cpuset[0]. You can forcibly move kernel threads into a given set (even pinned threads), and then force that set onto whatever cores you want. [0] http://www.kernel.org/doc/man-pages/online/pages/man7/cpuset...
Ah good stuff thanks posting that. I'll have to look into it, I haven't tried cpusets yet.
In the past I tried migrating kernel threads, the migration did work but system became unstable, so I gave up on that.
Re: The C10M problem
#38>Content Blocked (content_filter_denied) >Content Category: "Piracy/Copyright Concerns" I'm starting to use these blocks at my workplace as a measure of site quality (this will be a high quality article). Can someone dump the text for me?
Why would that page be a "Copyright Concern"?
Re: The C10M problem
#39Earlier quoted context omitted.
I believe it's what used to be called 'craftsmanship'. Taking pride in creating things that are efficient and not wasteful for no other reason than the desire to make the best product possible.
A beautifully carved chair may display excellent craftsmanship, but if you spend three months carving the world's most beautiful chair when the client asked for a dozen basic ladderbacks for a dinner party next Friday, you're not a very wise craftsman. Similarly, if your software runs in 1% of CPU on a typical customer's machine, spending 10x the time and resources to make it run in 0.1% is not laudable. Context is e…
>Similarly, if your software runs in 1% of CPU on a typical customer's machine, spending 10x the time and resources to make it run in 0.1% is not laudable.
No, but spending 1.2x the time and resources might be. That's not an unreasonable proposition; something written in Go, C# or Scala can run 10 to 100 times faster than the equivalent code in Ruby, but it certainly doesn't take 10 to 100 times longer to write the code.
It also conserves resources; you're reducing the amount of the world's non-renewable energy that your app consumes by up to 90%. You're also freeing up your users' machines to do more things simultaneously while running your program, potentially increasing the user's enjoyment of the system in the case of a desktop app.
Re: The C10M problem
#40At the risk of sounding dumb, aren't we still limited to 65,534 ports on an interface?
Port numbers must only be unique for ip:port pairs. A TCP connection is identified by the "quadruple" source_ip:source_port, dest_ip:dest_port. You can have as many connections as you want on the same source_ip on port 80 as long as there aren't 65,535 to the same dest_ip (ie as long as the quadruple is unique).
Also with IPv6 you can easily route a whole /64 net (264 IPs!) onto a single machine.