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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Pavel Pisa <pisa@fel.cvut.cz>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>, linux-rt-users@vger.kernel.org,
	Carsten Emde <c.emde@osadl.org>, linux-can@vger.kernel.org,
	Oliver Hartkopp <socketcan@hartkopp.net>,
	Jan Altenberg <Jan.Altenberg@osadl.org>,
	Pavel Hronek <hronepa1@fel.cvut.cz>
Subject: Re: CAN latency measuremet on AMD/Xilinx Zynq with PREEMP_RT - added
 threaded NAPI configuration
Message-ID: <20250417081254.EUqrBagT@linutronix.de>
References: <202501281629.27139.pisa@fel.cvut.cz>
 <20250129101709.XQuo8Jle@linutronix.de>
 <202501291304.15901.pisa@fel.cvut.cz>
 <202503281304.47808.pisa@fel.cvut.cz>
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In-Reply-To: <202503281304.47808.pisa@fel.cvut.cz>

On 2025-03-28 13:04:47 [+0100], Pavel Pisa wrote:
> Hello Marc and Sebastian,
>=20
Hi Pavel,

=E2=80=A6
> #!/bin/bash
>=20
> NAPI_PRIO=3D80
>=20
> if (( $# !=3D 1 )); then
>   echo "Need 1 argument (value 0 or 1)" >&2
>   exit 1
> fi
=E2=80=A6
> for ifc in can2 can3 can4 can5 ; do
>   echo $1 > /sys/class/net/$ifc/threaded
> done
>=20
> if [ $1 -eq 1 ] ; then
>   PIDS=3D$(ps -e | grep -E napi/can[0-9]+-[0-9] | tr -s ' ' | cut -d ' ' =
-f2)
>   for pid in $PIDS ; do
>     echo "Setting RT priority $NAPI_PRIO for $pid"
>     chrt -f --pid $NAPI_PRIO $pid
>   done
> fi

The IRQ thread should be limited to one CPU which is the same where the
IRQ it itself is set to. I don't think that this done the NAPI thread
automatically so it is probably free floating in the system.

Sebastian