From: Thomas Gleixner <email@example.com> To: Jakub Kicinski <firstname.lastname@example.org>, Sebastian Andrzej Siewior <email@example.com> Cc: firstname.lastname@example.org, Juri Lelli <email@example.com>, linux-rt-users <firstname.lastname@example.org>, Steven Rostedt <email@example.com>, LKML <firstname.lastname@example.org>, email@example.com, "David S. Miller" <firstname.lastname@example.org>, email@example.com Subject: Re: [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT Date: Fri, 14 May 2021 22:16:10 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <20210514115649.6c84fdc3@kicinski-fedora-PC1C0HJN> On Fri, May 14 2021 at 11:56, Jakub Kicinski wrote: > On Thu, 13 May 2021 00:28:02 +0200 Thomas Gleixner wrote: >> > --- >> > Alternatively __napi_schedule_irqoff() could be #ifdef'ed out on RT and >> > an inline provided which invokes __napi_schedule(). >> > >> > This was not chosen as it creates #ifdeffery all over the place and with >> > the proposed solution the code reflects the documentation consistently >> > and in one obvious place. >> >> Blame me for that decision. >> >> No matter which variant we end up with, this needs to go into all stable >> RT kernels ASAP. > > Mumble mumble. I thought we concluded that drivers used on RT can be > fixed, we've already done it for a couple drivers (by which I mean two). > If all the IRQ handler is doing is scheduling NAPI (which it is for > modern NICs) - IRQF_NO_THREAD seems like the right option. Yes. That works, but there are a bunch which do more than that IIRC. > Is there any driver you care about that we can convert to using > IRQF_NO_THREAD so we can have new drivers to "do the right thing" > while the old ones depend on this workaround for now? The start of this thread was about i40e_msix_clean_rings() which probably falls under the IRQF_NO_THREAD category, but I'm sure that there are others. So I chose the safe way for RT for now. > Another thing while I have your attention - ____napi_schedule() does > __raise_softirq_irqoff() which AFAIU does not wake the ksoftirq thread. > On non-RT we get occasional NOHZ warnings when drivers schedule napi > from process context, but on RT this is even more of a problem, right? > ksoftirqd won't run until something else actually wakes it up? Correct. I sent a patch for the r8152 usb network driver today which suffers from that problem. :) As I said there, we want a (debug/lockdep) check in __napi_schedule() whether soft interrupts are disabled, but let me have a look whether that check might make more sense directly in __raise_softirq_irqoff(). Thanks, tglx
next prev parent reply other threads:[~2021-05-14 20:16 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-11 6:09 [RT] Question about i40e threaded irq Juri Lelli 2021-05-11 6:24 ` Stefan Assmann 2021-05-11 7:46 ` Thomas Gleixner 2021-05-12 21:43 ` [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT Sebastian Andrzej Siewior 2021-05-12 22:28 ` Thomas Gleixner 2021-05-13 0:50 ` Steven Rostedt 2021-05-13 16:43 ` Steven Rostedt 2021-05-14 12:11 ` Thomas Gleixner 2021-05-14 18:56 ` Jakub Kicinski 2021-05-14 19:44 ` Alison Chaiken 2021-05-14 21:53 ` Thomas Gleixner 2021-05-14 20:16 ` Thomas Gleixner [this message] 2021-05-14 20:38 ` Jakub Kicinski 2021-05-13 5:12 ` Juri Lelli 2021-05-13 20:20 ` patchwork-bot+netdevbpf
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