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Torvalds: User-Space File-Systems, Toys, Misguided People

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  • #46
    Originally posted by Ze.. View Post
    Micro-kernels aren't slower , yes some were slower but that was due to poor design decisions to do with process handling and inter-process communication.
    What are you talking about? Of course they are slower, communicating through message passing will always be slower than communicating through shared memory. It's true that microkernels have worked hard on improving the speed of message passing, like grouping chunks of messages instead of passing them one by one for example. BUT IT IS STILL SLOWER. That's the price you pay for the safety of truly separated processes were if one crashes it won't bring down the system or even any other process, sometimes it's worth that price but again IT'S SLOWER. Microkernels has some undeniable benefits but speed certainly isn't one of them.

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    • #47
      Originally posted by XorEaxEax View Post
      What are you talking about? Of course they are slower, communicating through message passing will always be slower than communicating through shared memory.
      Indeed. I was reading about the latest version of Minix yesterday after reading this thread and one thing one article said was that writing to an I/O port through the microkernel only took 500 nanoseconds. Which doesn't sound so bad until you realise that it's typically 1,000-1,500 clock cycles on a modern CPU.

      Fortunately it's not something that drivers do often (I'm guessing 90+% of I/O these days is memory mapped) and I/O writes are slow anyway, but it's still a pretty significant amount of time for what would otherwise be a simple instruction in the kernel.

      That said, kernel performance probably doesn't matter much in normal desktop use; it's much more important in specialised uses like high-performance web servers where you really don't want to be taking the hit of continually going in and out of user space to send network packets.

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      • #48
        Just to clarify: ZFS on linux is not FUSE based as some people say. There was a zfs fuse implementation but ZOL is far more advanced and a lot of people using it successfully in production. To read about the license incompatibility issue see: http://zfsonlinux.org/faq.html#WhatA...LicensingIssue . Btw. a lot of people believe there is even a legal way to include the zfs code into mainline kernel, but probably a court has to decide this (hello oracle). Nevertheless zfs is super stable (we use it in production for more than two years).

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        • #49
          Originally posted by dreh23 View Post
          Just to clarify: ZFS on linux is not FUSE based as some people say. There was a zfs fuse implementation but ZOL is far more advanced and a lot of people using it successfully in production. To read about the license incompatibility issue see: http://zfsonlinux.org/faq.html#WhatA...LicensingIssue . Btw. a lot of people believe there is even a legal way to include the zfs code into mainline kernel, but probably a court has to decide this (hello oracle). Nevertheless zfs is super stable (we use it in production for more than two years).
          Funnily enough ZOL is not installable on Debian if you want virt-sparsify on your machine. It depends on fuse-zfs

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