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doc/theses/thierry_delisle_PhD/comp_II/comp_II.tex
r5569a31 r912ccbcf 447 447 $select$ entails significant complexity and is being replaced in UNIX operating-systems, which make it a less interesting alternative. 448 448 Another popular interface is $epoll$\cite{epoll}, which is supposed to be cheaper than $select$. 449 However, $epoll$ also does not handle the file system and seems to have problem to linux pipes and $TTY$s\cit. 449 However, $epoll$ also does not handle the file system and anectodal evidence suggest it has problem with linux pipes and $TTY$s. 450 A popular cross-platform alternative is $libuv$\cite{libuv}, which offers asynchronous sockets and asynchronous file system operations (among other features). 451 However, as a full-featured library it includes much more than I need and could conflict with other features of \CFA unless significant effort is made to merge them together. 450 452 A very recent alternative that I am investigating is $io_uring$\cite{io_uring}. 451 It claims to address some of the issues with $epoll$ but is too recent to be confident that it does. 452 Finally, a popular cross-platform alternative is $libuv$\cite{libuv}, which offers asynchronous sockets and asynchronous file system operations (among other features). 453 However, as a full-featured library it includes much more than I need and could conflict with other features of \CFA unless significant effort is made to merge them together. 453 It claims to address some of the issues with $epoll$ and my early investigating suggest that the claim is accurate. 454 $io_uring$ uses a much more general approach where system calls are register to a queue and later executed by the kernel, rather than relying on system calls to return an error instead of blocking and subsequently waiting for changes on file descriptors. 455 I believe this approach allows for fewer problems, \eg the manpage for $open$\cite{open} states: 456 \begin{quote} 457 Note that [the $O_NONBLOCK$ flag] has no effect for regular files and block devices; 458 that is, I/O operations will (briefly) block when device activity is required, regardless of whether $O_NONBLOCK$ is set. 459 Since $O_NONBLOCK$ semantics might eventually be implemented, applications should not depend upon blocking behavior when specifying this flag for regular files and block devices. 460 \end{quote} 461 This makes approach based on $epoll$/$select$ less reliable since they may not work for every file descriptors. 462 For this reason, I plan to use $io_uring$ as the OS abstraction for the \CFA runtime, unless further work shows problems I haven't encountered yet. 463 However, only a small subset of the features are available in Ubuntu as of April 2020\cite{wiki:ubuntu-linux}, which will limit performance comparisons. 464 I do not believe this will affect the comparison result. 454 465 455 466 \paragraph{Event Engine} … … 477 488 % =============================================================================== 478 489 \section{Discussion} 479 490 I believe that runtime system and scheduling are still open topics. 491 Many ``state of the art'' production frameworks still use single threaded event-loops because of performance considerations, \eg \cite{nginx-design}, and, to my knowledge, no wideyl available system language offers modern threading facilities. 492 I believe the proposed work offers a novel runtime and scheduling package, where existing work only offers fragments that users must assemble themselves when possible. 480 493 481 494 % =============================================================================== 482 495 % =============================================================================== 483 496 \section{Timeline} 484 497 \begin{center} 498 \begin{tabular}{ | r @{--} l | p{4in} | } 499 \hline May 2020 & October 2020 & Creation of the performance benchmark. \\ 500 \hline November 2020 & March 2021 & Completion of the implementation. \\ 501 \hline March 2021 & April 2021 & Final Performance experiments. \\ 502 \hline May 2017 & August 2021 & Thesis writing and defense. \\ 503 \hline 504 \end{tabular} 505 \end{center} 485 506 486 507 % B I B L I O G R A P H Y
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