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

[jabl]

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?

[onlyLinuxLuvUBack]

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

[Alex/AT]

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

[JEBjames]

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"

[Alex/AT]

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.

[phoronix]

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