On 2014-02-23, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Thu, 20 Feb 2014, Peter Hurley wrote:
>> Using Alan's idea to mock up a latency test, I threw together a test
>> jig using two computers running 3.14-rc1 and my fwserial driver
>> (modified to not aggregrate writes) in raw mode where the target does
>> this:
>
> This is a complete pointless test.
No, it isn't. It tested exactly what it was supposed to test: latency
between the driver pushing bytes to the line discipline and user-space
read waking up.
> Use a bog standard 8250 UART on the PC and connect a microcontroller
> on the other end which serves you an continous stream of data at
> 115200 Baud.
>
> There is no way you can keep up with that without the low latency
> option neither on old and nor on new machines if you have enough
> other stuff going on in the system.
That makes no sense. Enabling the low-latency option historically
made it _harder_ to keep up since it caused more overhead in the form
buffer processing and context switches.
--
Grant Edwards grant.b.edwards Yow! Look into my eyes and
at try to forget that you have
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