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Linux Serial Console Driver Lands Patch For Possible ~25% Performance Improvement

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  • jabl
    replied
    Wonder if this would affect 'virtual' serial ports as well, as commonly seen on server platforms where you have a virtual serial console accessible via the BMC? Or is it only for 'real' hardware UART chips?

    Leave a comment:


  • onlyLinuxLuvUBack
    replied
    Originally posted by Alex/AT View Post
    Basically this means controller is sending bytes faster than polling sender can feed it.
    It's not polling in a tight loop, it's rescheduled. And the poller is not scheduled in intervals short enough on specific machine it seems.

    OR the UART (or its emulation by i.e. BMC) is so crazy that it doesn't bring the related 'buffer empty' bit to 'empty' state immediately after transmitting the buffered byte, like nobody ever expected someone no less crazy would be sending stuff at high speeds without FIFO in polling mode
    a phoronix bar chart and benchmark will settle this

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  • Alex/AT
    replied
    Originally posted by JEBjames View Post
    Not sure how it could make that big a speed difference as quoted in the article?
    Basically this means controller is sending bytes faster than polling sender can feed it.
    It's not polling in a tight loop, it's rescheduled. And the poller is not scheduled in intervals short enough on specific machine it seems.

    OR the UART (or its emulation by i.e. BMC) is so crazy that it doesn't bring the related 'buffer empty' bit to 'empty' state immediately after transmitting the buffered byte, like nobody ever expected someone no less crazy would be sending stuff at high speeds without FIFO in polling mode
    Last edited by Alex/AT; 12 January 2022, 05:32 PM.

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  • JEBjames
    replied
    The UART FIFO queue can reduces CPU load (fewer interrupts). But even pre-486 PCs can easily max out a 16550 sending a byte at a time?

    Not sure how it could make that big a speed difference as quoted in the article?

    Task switching that broken? Insert Spectre/Meltdown/RandomCPUBugOfTheWeek?

    I'm confused.

    Michael typo: "cosnole"

    Leave a comment:


  • Alex/AT
    replied
    16550 UARTs FIFO support was missing all that time?
    Holy moly. I thought it's 2022 already, but it's more like 1982 there then.

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  • Linux Serial Console Driver Lands Patch For Possible ~25% Performance Improvement

    Phoronix: Linux Serial Console Driver Lands Patch For Possible ~25% Performance Improvement

    It's not an area of Linux hardware performance we normally look at, but thanks to a Red Hat engineer discovering very low serial console performance, there is an improvement queued up for introduction in Linux 5.17.....

    https://www.phoronix.com/scan.php?pa...ial-16550-FIFO
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