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Message-ID: <MWHPR11MB129321759864A20827BE04DDF1469@MWHPR11MB1293.namprd11.prod.outlook.com> Date: Thu, 25 May 2023 00:16:54 +0000 From: "Nambiar, Amritha" <amritha.nambiar@...el.com> To: Jakub Kicinski <kuba@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>, "Kanzenbach, Kurt" <kurt.kanzenbach@...utronix.de>, Paolo Abeni <pabeni@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, "Samudrala, Sridhar" <sridhar.samudrala@...el.com> Subject: RE: [RFC PATCH 1/2] net: Add sysfs files for threaded NAPI. > -----Original Message----- > From: Jakub Kicinski <kuba@...nel.org> > Sent: Wednesday, May 24, 2023 9:25 PM > To: Sebastian Andrzej Siewior <bigeasy@...utronix.de> > Cc: netdev@...r.kernel.org; Eric Dumazet <edumazet@...gle.com>; > Kanzenbach, Kurt <kurt.kanzenbach@...utronix.de>; Paolo Abeni > <pabeni@...hat.com>; Thomas Gleixner <tglx@...utronix.de> > Subject: Re: [RFC PATCH 1/2] net: Add sysfs files for threaded NAPI. > > On Wed, 24 May 2023 13:12:58 +0200 Sebastian Andrzej Siewior wrote: > > I've been looking into threaded NAPI. One awkward thing to do is > > to figure out the thread names, pids in order to adjust the thread > > priorities and SMP affinity. > > On PREEMPT_RT the NAPI thread is treated (by the user) the same way as > > the threaded interrupt which means a dedicate CPU affinity for the > > thread and a higher task priority to be favoured over other tasks on the > > CPU. Otherwise the NAPI thread can be preempted by other threads > leading > > to delays in packet delivery. > > Having to run ps/ grep is awkward to get the PID right. It is not easy > > to match the interrupt since there is no obvious relation between the > > IRQ and the NAPI thread. > > NAPI threads are enabled often to mitigate the problems caused by a > > "pending" ksoftirqd (which has been mitigated recently by doing softiqrs > > regardless of ksoftirqd status). There is still the part that the NAPI > > thread does not use softnet_data::poll_list. > > This needs to go to the netdev netlink family, not sysfs. > There's much more information about NAPI to expose and sysfs will > quickly start showing its limitations. Based on the discussion in https://lore.kernel.org/netdev/c8476530638a5f4381d64db0e024ed49c2db3b02.camel@gmail.com/T/#m00999652a8b4731fbdb7bf698d2e3666c65a60e7 , I am working on a patch series (will post RFCs next week), to extend the netdev-genl interface to expose napi_ids and associated queues. The patch series will enable support for retrieving napi information contained in the netdev struct, such as napi id, queue/queue-set (both RX and TX) associated with each napi instance etc. I figure this requirement for exposing napi thread to PID association can be done as a follow-on/extension to my series.
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