Hi Willem, On Mon, May 13, 2024 at 10:09 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > Luiz Augusto von Dentz wrote: > > Hi Willem, > > > > On Mon, May 13, 2024 at 9:32 PM Willem de Bruijn > > <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > > > > Jakub Kicinski wrote: > > > > On Mon, 13 May 2024 18:09:31 -0400 Luiz Augusto von Dentz wrote: > > > > > > There is one more warning in the Intel driver: > > > > > > > > > > > > drivers/bluetooth/btintel_pcie.c:673:33: warning: symbol 'causes_list' > > > > > > was not declared. Should it be static? > > > > > > > > > > We have a fix for that but I was hoping to have it in before the merge > > > > > window and then have the fix merged later. > > > > > > > > > > > It'd also be great to get an ACK from someone familiar with the socket > > > > > > time stamping (Willem?) I'm not sure there's sufficient detail in the > > > > > > commit message to explain the choices to: > > > > > > - change the definition of SCHED / SEND to mean queued / completed, > > > > > > while for Ethernet they mean queued to qdisc, queued to HW. > > > > > > > > > > hmm I thought this was hardware specific, it obviously won't work > > > > > exactly as Ethernet since it is a completely different protocol stack, > > > > > or are you suggesting we need other definitions for things like TX > > > > > completed? > > > > > > > > I don't know anything about queuing in BT, in terms of timestamping > > > > the SEND - SCHED difference is supposed to indicate the level of > > > > host delay or host congestion. If the queuing in BT happens mostly in > > > > the device HW queue then it may make sense to generate SCHED when > > > > handing over to the driver. OTOH if the devices can coalesce or delay > > > > completions the completion timeout may be less accurate than stamping > > > > before submitting to HW... I'm looking for the analysis that the choices > > > > were well thought thru. > > > > > > SCM_TSTAMP_SND is taken before an skb is passed to the device. > > > This matches request SOF_TIMESTAMPING_TX_SOFTWARE. > > > > > > A timestamp returned on transmit completion is requested as > > > SOF_TIMESTAMPING_TX_HARDWARE. We do not have a type for a software > > > timestamp taken at tx completion cleaning. If anything, I would think > > > it would be a passes as a hardware timestamp. > > > > In that case I think we probably misinterpret it, at least I though > > that TX_HARDWARE would really be a hardware generated timestamp using > > it own clock > > It normally is. It is just read from the tx descriptor on completion. > > We really don't have a good model for a software timestamp taken at > completion processing. > > It may be worthwhile more broadly, especially for devices that do not > support true hardware timestamps. > > Perhaps we should add an SCM_TSTAMP_TXCOMPLETION for this case. And a > new SOF_TIMESTAMPING option to go with it. Similar to what we did for > SCM_STAMP_SCHED. > > > if you are saying that TX_HARDWARE is just marking the > > TX completion of the packet at the host then we can definitely align > > with the current exception, that said we do have a command to actually > > read out the actual timestamp from the BT controller, that is usually > > more precise since some of the connection do require usec precision > > which is something that can get skew by the processing of HCI events > > themselves, well I guess we use that if the controller supports it and > > if it doesn't then we do based on the host timestamp when processing > > the HCI event indicating the completion of the transmission. > > > > > Returning SCHED when queuing to a device and SND later on receiving > > > completions seems like not following SO_TIMESTAMPING convention to me. > > > But I don't fully know the HCI model. > > > > > > As for the "experimental" BT_POLL_ERRQUEUE. This is an addition to the > > > ABI, right? So immutable. Is it fair to call that experimental? > > > > I guess you are referring to the fact that sockopt ID reserved to > > BT_POLL_ERRQUEUE cannot be reused anymore even if we drop its usage in > > the future, yes that is correct, but we can actually return > > ENOPROTOOPT as it current does: > > > > if (!bt_poll_errqueue_enabled()) > > return -ENOPROTOOPT > > I see. Once applications rely on a feature, it can be hard to actually > deprecate. But in this case it may be possible. > > > Anyway I would be really happy to drop it so we don't have to worry > > about it later. > > > > > It might be safer to only suppress the sk_error_report in > > > sock_queue_err_skb. Or at least in bt_sock_poll to check the type of > > > all outstanding errors and only suppress if all are timestamps. > > > > Or perhaps we could actually do that via poll/epoll directly? Not that > > it would make it much simpler since the library tends to wrap the > > usage of poll/epoll but POLLERR meaning both errors or errqueue events > > is sort of the problem we are trying to figure out how to process them > > separately. > > The process would still be awoken, of course. If bluetoothd can just > be modified to ignore the reports, that would indeed be easiest from > a kernel PoV. @Pauli Virtanen tried that but apparently it would keep waking up the process until the errqueue is fully read, maybe we are missing something, or glib is not really doing a good job wrt to poll/epoll handling. -- Luiz Augusto von Dentz
