On 4/12/22 8:32 PM, Eric Dumazet wrote: > On Tue, Apr 12, 2022 at 7:27 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >> >> On 4/12/22 8:19 PM, Eric Dumazet wrote: >>> On Tue, Apr 12, 2022 at 7:12 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>> >>>> On 4/12/22 8:05 PM, Eric Dumazet wrote: >>>>> On Tue, Apr 12, 2022 at 7:01 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>>> >>>>>> On 4/12/22 7:54 PM, Eric Dumazet wrote: >>>>>>> On Tue, Apr 12, 2022 at 6:26 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>>>>> >>>>>>>> On 4/12/22 6:40 PM, Eric Dumazet wrote: >>>>>>>>> >>>>>>>>> On 4/12/22 13:26, Jens Axboe wrote: >>>>>>>>>> Hi, >>>>>>>>>> >>>>>>>>>> If we accept a connection directly, eg without installing a file >>>>>>>>>> descriptor for it, or if we use IORING_OP_SOCKET in direct mode, then >>>>>>>>>> we have a socket for recv/send that we can fully serialize access to. >>>>>>>>>> >>>>>>>>>> With that in mind, we can feasibly skip locking on the socket for TCP >>>>>>>>>> in that case. Some of the testing I've done has shown as much as 15% >>>>>>>>>> of overhead in the lock_sock/release_sock part, with this change then >>>>>>>>>> we see none. >>>>>>>>>> >>>>>>>>>> Comments welcome! >>>>>>>>>> >>>>>>>>> How BH handlers (including TCP timers) and io_uring are going to run >>>>>>>>> safely ? Even if a tcp socket had one user, (private fd opened by a >>>>>>>>> non multi-threaded program), we would still to use the spinlock. >>>>>>>> >>>>>>>> But we don't even hold the spinlock over lock_sock() and release_sock(), >>>>>>>> just the mutex. And we do check for running eg the backlog on release, >>>>>>>> which I believe is done safely and similarly in other places too. >>>>>>> >>>>>>> So lets say TCP stack receives a packet in BH handler... it proceeds >>>>>>> using many tcp sock fields. >>>>>>> >>>>>>> Then io_uring wants to read/write stuff from another cpu, while BH >>>>>>> handler(s) is(are) not done yet, >>>>>>> and will happily read/change many of the same fields >>>>>> >>>>>> But how is that currently protected? >>>>> >>>>> It is protected by current code. >>>>> >>>>> What you wrote would break TCP stack quite badly. >>>> >>>> No offense, but your explanations are severely lacking. By "current >>>> code"? So what you're saying is that it's protected by how the code >>>> currently works? From how that it currently is? Yeah, that surely >>>> explains it. >>>> >>>>> I suggest you setup/run a syzbot server/farm, then you will have a >>>>> hundred reports quite easily. >>>> >>>> Nowhere am I claiming this is currently perfect, and it should have had >>>> an RFC on it. Was hoping for some constructive criticism on how to move >>>> this forward, as high frequency TCP currently _sucks_ in the stack. >>>> Instead I get useless replies, not very encouraging. >>>> >>>> I've run this quite extensively on just basic send/receive over sockets, >>>> so it's not like it hasn't been run at all. And it's been fine so far, >>>> no ill effects observed. If we need to tighten down the locking, perhaps >>>> a valid use would be to simply skip the mutex and retain the bh lock for >>>> setting owner. As far as I can tell, should still be safe to skip on >>>> release, except if we need to process the backlog. And it'd serialize >>>> the owner setting with the BH, which seems to be your main objection in. >>>> Mostly guessing here, based on the in-depth replies. >>>> >>>> But it'd be nice if we could have a more constructive dialogue about >>>> this, rather than the weird dismisiveness. >>>> >>>> >>> >>> Sure. It would be nice that I have not received such a patch series >>> the day I am sick. >> >> I'm sorry that you are sick - but if you are not in a state to reply, >> then please just don't. It sets a bad example. It was sent to the list, >> not to you personally. > > I tried to be as constructive as possible, and Jakub pinged me about Are you serious?! I don't think I've ever received less constructive feedback in 20+ years of working on the kernel. > this series, > so I really thought Jakub was okay with it. > > So I am a bit concerned. I did show it to Jakub a week or so ago, probably that was why. But why the concern?! It's just a patchseries proposed for discussion. Something that happens every day. >> Don't check email then, putting the blame on ME for posting a patchset >> while you are sick is uncalled for and rude. If I had a crystal ball, I >> would not be spending my time working on the kernel. You know what >> would've been a better idea? Replying that you are sick and that you are >> sorry for being an ass on the mailing list. > > Wow. Putting the blame on me for your emails, since I posted a patchset while you're sick, is just rude. -- Jens Axboe
