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> Amdahl's law is about accelerating one job by parallelising it, Amdahl's law is about the limitations of improving the speed of something, but not necessari

> Amdahl's law is about accelerating one job by parallelising it, Amdahl's law is about the limitations of improving the speed of something, but not necessarily through parallelization. Its main point is that if you have some overall task, and you then speed up some subtask within it, the improvement to the overall time is limited to the contribution from the subtask. In context of pcwalton's comment, I think they meant that thread creation time may be tiny compared to the amount of time a newly created thread will do work in a server context. If that is the case, improving the thread creation time will have limited benefit to serve time.

pron 6y ago
> Amdahl's law is about the limitations of improving the speed of something, but not necessarily through parallelization. Right, but the goal here is not to improve the speed of something, but rather to handle as many different, mostly independent somethings as possible, without necessarily improving their speed (latency), at all. Amdahl's law comes into effect in the delta between mostly and completely. > they meant that thread creation time may be tiny compared to the amount of time a newly created thread will do work in a server context. If that is the case, improving the thread creation time will have limited benefit to serve time. Right, this is the same argument as for the context-switch overhead. Still, I have to say that both virtual thread creation and context-switching are much better than for OS thread, but the point of the post was to show that in many common use cases that is not where most of the benefit comes from; rather it comes from the number of threads you can have. For example, if thread creation time was high but you could create millions of them, you could create all of them up front and pool them and still get most/all of the benefits. But if thread creation time was low but you could only have a few thousand, then you'd still lose big because of Little's law.
- scott_s 6y ago
  Agreed, strongly. I was just concerned the original comment may not have been fully understood.

pron 6y ago

> Amdahl's law is about the limitations of improving the speed of something, but not necessarily through parallelization. Right, but the goal here is not to improve the speed of something, but rather to handle as many different, mostly independent somethings as possible, without necessarily improving their speed (latency), at all. Amdahl's law comes into effect in the delta between mostly and completely. > they meant that thread creation time may be tiny compared to the amount of time a newly created thread will do work in a server context. If that is the case, improving the thread creation time will have limited benefit to serve time. Right, this is the same argument as for the context-switch overhead. Still, I have to say that both virtual thread creation and context-switching are much better than for OS thread, but the point of the post was to show that in many common use cases that is not where most of the benefit comes from; rather it comes from the number of threads you can have. For example, if thread creation time was high but you could create millions of them, you could create all of them up front and pool them and still get most/all of the benefits. But if thread creation time was low but you could only have a few thousand, then you'd still lose big because of Little's law.

scott_s 6y ago
Agreed, strongly. I was just concerned the original comment may not have been fully understood.