Messages in this thread | | | Date | Mon, 3 Jul 2023 15:50:55 +0200 | Subject | Re: [PATCH RFC net-next 0/4] net: page_pool: a couple assorted optimizations | From | Alexander Lobakin <> |
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From: Jakub Kicinski <kuba@kernel.org> Date: Sat, 1 Jul 2023 17:01:55 -0700
> On Thu, 29 Jun 2023 17:23:01 +0200 Alexander Lobakin wrote: >> #3: new, prereq to #4. Add NAPI state flag, which would indicate >> napi->poll() is running right now, so that napi->list_owner would >> point to the CPU where it's being run, not just scheduled; >> #4: new. In addition to recycling skb PP pages directly when @napi_safe >> is set, check for the flag from #3, which will mean the same if >> ->list_owner is pointing to us. This allows to use direct recycling >> anytime we're inside a NAPI polling loop or GRO stuff going right >> after it, covering way more cases than is right now. > > You know NAPI pretty well so I'm worried I'm missing something.
I wouldn't say I know it well :D
> I don't think the new flag adds any value. NAPI does not have to > be running, you can drop patch 3 and use in_softirq() instead of > the new flag, AFAIU.
That's most likely true for the patch 4 case, but I wanted to add some flag for wider usage. For example, busy polling relies on whether ->poll() returned whole budget to decide whether interrupts were reenabled to avoid possible concurrent access, but I wouldn't say it's precise enough. napi_complete_done() doesn't always return true. OTOH, the new flag or, more precisely, flag + list_owner combo would tell for sure.
> > The reason I did not do that is that I wasn't sure if there is no > weird (netcons?) case where skb gets freed from an IRQ :(
Shouldn't they use dev_kfree_skb_any() or _irq()? Usage of plain kfree_skb() is not allowed in the TH :s
Anyway, if the flag really makes no sense, I can replace it with in_softirq(), it's my hobby to break weird drivers :D
Thanks, Olek
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