Messages in this thread | | | Date | Wed, 11 Nov 2015 14:19:56 -0500 (EST) | Subject | Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller | From | David Miller <> |
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From: Måns Rullgård <mans@mansr.com> Date: Wed, 11 Nov 2015 19:17:07 +0000
> David Miller <davem@davemloft.net> writes: > >> From: Måns Rullgård <mans@mansr.com> >> Date: Wed, 11 Nov 2015 19:09:19 +0000 >> >>> David Miller <davem@davemloft.net> writes: >>> >>>> From: Måns Rullgård <mans@mansr.com> >>>> Date: Wed, 11 Nov 2015 18:25:05 +0000 >>>> >>>>> If the TX DMA channel is idle when start_xmit is called, it can be >>>>> started immediately. Checking the DMA status and starting it if >>>>> idle has to be done atomically somehow. >>>> >>>> ->ndo_start_xmit() is guaranteed to be invoked atomically, protected >>>> by the TX queue spinlock. >>> >>> Yes, but the DMA needs to be restarted from some other context if it was >>> busy when start_xmit checked. >> >> Then you can probably use the TXQ lock in the interrupt handler just for >> that. > > That seems a bit heavy-handed when the critical section for this is only > a tiny part of the start_xmit function.
Then what synchornization primitive other than spin locks are you going to use for this?
My point is that there is a spinlock the core code is _already_ taking, unconditionally, when ->ndo_start_xmit() executes. And you can therefore take advantage of that rather than using another lock of your own.
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