Re: BlueZ Central to Peripheral latency issue

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Mathias,

On Tue, Jul 2, 2019 at 3:33 PM Mathias Baert <mathiasrobaert@gmail.com> wrote:
>
> Hi,
>
> We are using the BlueZ 5.48 version on a Raspberry PI with Raspbian Stretch 9.1.
>
> The setup is this PI connected with a Nordic Semiconductor nRF52840
> device, via an IPv6 over BLE connection. The connection is using a
> connection interval of 7.5 ms. Via throughput measurements with iperf,
> both ways (central to peripheral and peripheral to central), we are
> able to achieve maximally ~ 100 kbps (using the 1 Mbps PHY).
>
> However, when looking into individual packet exchanges, we notice a
> significant delay (up to 1 sec) in the RTT when pinging from the
> peripheral to the BlueZ central and back. We also see a huge
> fluctuation in this value and it also depends on the intervals at
> which the pings are fired (lower throughput gives a much higher
> average individual latency). When firing ping packets at a 1 sec
> interval, it is definitely visible.
>
> When looking into this, we found that the latency between the
> peripheral and the central is quite stable and low enough. But the
> latency between the central and peripheral is fluctuating a lot and is
> generally quite high. Is this something you have noticed before? We
> think that it could be a scheduling issue on the kernel, where higher
> throughput gives more priority to Bluetooth communication?

So I assume this is using the experimental IPSP support with Zephyr as
peripheral? Usually, the Linux side is quite a bit more complex so it
is not surprising it can take more time but not 1 sec. so it got to be
something that is causing the extra lag, perhaps you can paste the
actual commands you are using to ping one another.

-- 
Luiz Augusto von Dentz