On 08.03.2021 15:56:53, Marc Kleine-Budde wrote: > > > meanwhile this patch hit v5.10.x stable and caused a performance > > > degradation on our use case: > > > > > > It's an embedded ARM system, 4x Cortex A53, with an SPI attached CAN > > > controller. CAN stands for Controller Area Network and here used to > > > connect to some automotive equipment. Over CAN an ISOTP (a CAN-specific > > > Transport Protocol) transfer is running. With this patch, we see CAN > > > frames delayed for ~6ms, the usual gap between CAN frames is 240µs. > > > > > > Reverting this patch, restores the old performance. > > > > > > What is the best way to solve this dilemma? Identify the critical path > > > in our use case? Is there a way we can get around the irqsave in > > > led_trigger_event()? > > > > > > > Probably, we can change from rwlock to rcu here, POC code as follow, > > only compile tested. Marc, could you see whether this help the > > performance on your platform? Please note that I haven't test it in a > > running kernel and I'm not that familir with led subsystem, so use it > > with caution ;-) > > > > (While at it, I think maybe we miss the leddev_list_lock in net/mac80211 > > in the patch) > > I can confirm, this patch basically restores the old performance. Hmmm - it first looked OK, now it doesn't - let me do some better testing. Sorry for the noise, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
Attachment:
signature.asc
Description: PGP signature
