Changeset d0fcc82 for doc/theses/thierry_delisle_PhD

Timestamp:

Jul 29, 2022, 10:49:52 AM (21 months ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, ast-experimental, master, pthread-emulation

Children:

b507dcd

Parents:

c4c8571

Message:

New version of the abstract

File:

• doc/theses/thierry_delisle_PhD/thesis/text/front.tex (modified) (1 diff)

doc/theses/thierry_delisle_PhD/thesis/text/front.tex

@@ -123 +123 @@
 \begin{center}\textbf{Abstract}\end{center}
 
-This is the abstract.
-
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+User-Level threading (M:N) is gaining popularity over kernel-level threading (1:1) in many programming languages.
+The user-level approach is often a better mechanism to express complex concurrent applications by efficiently running 10,000+ threads on multi-core systems.
+Indeed, over-partitioning into small work-units significantly eases load balancing while providing user threads for each unit of work offers greater freedom to the programmer.
+To manage these high levels of concurrency, the underlying runtime must efficiently schedule many user threads across a few kernel threads;
+which begs of the question of how many kernel threads are needed and when should the need be re-evaliated.
+Furthermore, the scheduler must prevent kernel threads from blocking, otherwise user-thread parallelism drops, and put idle kernel-threads to sleep to avoid wasted resources.
+Finally, the scheduling system must provide fairness to prevent a user thread from monopolizing a kernel thread;
+otherwise other user threads can experience short/long term starvation or kernel threads can deadlock waiting for events to occur.
+
+This thesis analyses multiple scheduler systems, where each system attempts to fulfill the necessary requirements for user-level threading.
+The predominant technique for manage high levels of concurrency is sharding the ready-queue with one queue per kernel-threads and using some form of work stealing/sharing to dynamically rebalance workload shifts.
+Fairness can be handled through preemption or ad-hoc solutions, which leads to coarse-grained fairness and pathological cases.
+Preventing kernel blocking is accomplish by transforming kernel locks and I/O operations into user-level operations that do not block the kernel thread or spin up new kernel threads to manage the blocking.
+
+After selecting specific approaches to these scheduling issues, a complete implementation was created and tested in the \CFA (C-for-all) runtime system.
+\CFA is a modern extension of C using user-level threading as its fundamental threading model.
+As one of its primary goals, \CFA aims to offer increased safety and productivity without sacrificing performance.
+The new scheduler achieves this goal by demonstrating equivalent performance to work-stealing schedulers while offering better fairness.
+This is achieved through several optimization that successfully eliminate the cost of the additional fairness, some of these optimization relying on interesting hardware optimizations present on most modern cpus.
+This work also includes support for user-level \io, allowing programmers to have many more user-threads blocking on \io operations than there are \glspl{kthrd}.
+The implementation is based on @io_uring@, a recent addition to the Linux kernel, and achieves the same performance and fairness.
+To complete the picture, the idle sleep mechanism that goes along is presented.
+
+
 
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