Hello,



More of my philosophy about my lock-free inventions and about tail
latency and more..

I am a white arab and i think i am smart since i have also invented many scalable algorithms..


I have just posted about some of my new inventions, so read about them carefully here:

https://groups.google.com/g/alt.culture.morocco/c/YLnuhRSGuY8


And Bonita Montero has just answered me the following:

Lock-free queues totally suck since they have to
be polled. The only lock-free structure that is
useful is a lock-free stack for pooing objects and
handling back items to a thread like with modern
memory-allocators.

And i have just answered her the following:

Typically, polling a lock-free queue works best when
the queue nearly always has entries, a blocking queue
works best when the queue is nearly always empty.
A downside of blocking queues is latency, typically of
the order of 2-20 uS, due to kernel signaling. This can
be mitigated by designing the system so that the work done
by the consumer threads on each queued item takes much
longer than this interval.The downside of non-blocking queues
is the waste of CPU and memory bandwidth while polling an
empty queue. This can be mitigated by designing the system
so that the queue is rarely empty.

So Bonita Montero has just answered me the following:

Forget it - no one wants to poll a queue. Having limited
polling with spinning for a while is the best of both sides.

And i have just answered her the following:

You have to understand that lockfree has advantages
and disadvantages, so since lock-free queue works best
when the queue nearly always has entries, so it is used best
on those kind of situations, and for you wanting to have
limited polling with spinning for a while.., i think you
have to understand that lockfree comes with a number of
advantages like it is not prone to deadlock and it is
Pre-emption tolerant (so it is good at convoy-avoidance) etc.
so you have to take into account those factors too so that to
make a good choice depending > on the situation or the context.

Also i have to talk more about tail latency, so first i have to define
more what is Tail latency, and here it is:

Tail latency, also known as high-percentile latency, refers to high
latencies that clients see fairly infrequently. ... There are many
causes of tail latency in the world, including contention, garbage
collection, packet loss, host failure, and weird stuff operating
systems do in the background.

So i think that wait-free queues are better than lock-free queues
in Tail latency, and you can read the following article so that to
notice it:

Throughput vs Latency and Lock-Free vs Wait-Free

http://concurrencyfreaks.blogspot.com/2016/08/throughput-vs-latency-and-lock-free-vs.html

But i can finally say that lock-free queues are still useful.



Thank you,
Amine Moulay Ramdane.

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