Re: [PATCH] serial: imx: reduce RX interrupt frequency

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 05.01.2022 16:00:34, Sergey Organov wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> 
> > On Tue, Jan 04, 2022 at 11:32:03AM +0100, Tomasz Moń wrote:
> >> Triggering RX interrupt for every byte defeats the purpose of aging
> >> timer and leads to interrupt starvation at high baud rates.
> >> 
> >> Increase receiver trigger level to 8 to increase the minimum period
> >> between RX interrupts to 8 characters time. The tradeoff is increased
> >> latency. In the worst case scenario, where RX data has intercharacter
> >> delay slightly less than aging timer (8 characters time), it can take
> >> up to 63 characters time for the interrupt to be raised since the
> >> reception of the first character.
> >
> > Why can't you do this dynamically based on the baud rate so as to always
> > work properly for all speeds without increased delays for slower ones?
> 
> I don't like the idea of dynamic threshold as I don't think increased
> complexity is worth it.
> 
> In fact the threshold works "properly" on any baud rate, as maximum
> latency is proportional to the current baud rate, and if somebody does
> care about *absolute* latency, increasing baud rate is the primary
> solution.

Nope - this only works if you have both sides under control.... Which is
not the case in our $CUSTROMER's use case.

Marc

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