On Thu, Aug 31, 2017 at 10:10 PM, Alexei Starovoitov <alexei.starovoi...@gmail.com> wrote: > On Thu, Aug 31, 2017 at 05:00:13PM -0400, Willem de Bruijn wrote: >> From: Willem de Bruijn <will...@google.com> >> >> Documentation for this feature was missing from the patchset. >> Copied a lot from the netdev 2.1 paper, addressing some small >> interface changes since then. >> >> Signed-off-by: Willem de Bruijn <will...@google.com> > ... >> +Notification Batching >> +~~~~~~~~~~~~~~~~~~~~~ >> + >> +Multiple outstanding packets can be read at once using the recvmmsg >> +call. This is often not needed. In each message the kernel returns not >> +a single value, but a range. It coalesces consecutive notifications >> +while one is outstanding for reception on the error queue. >> + >> +When a new notification is about to be queued, it checks whether the >> +new value extends the range of the notification at the tail of the >> +queue. If so, it drops the new notification packet and instead increases >> +the range upper value of the outstanding notification. > > Would it make sense to mention that max notification range is 32-bit? > So each 4Gbyte of xmit bytes there will be a notification. > In modern 40Gbps NICs it's not a lot. Means that there will be > at least one notification every second. > Or I misread the code?
You're right. The doc does mention that the counter and range are 32-bit. I can state more explicitly that that bounds the working set size to 4GB. Do you expect this to be problematic? Processing a single notification per 4GB of data should not be a significant cost in itself. > Thanks for the doc! Thanks for reviewing :) > > Acked-by: Alexei Starovoitov <a...@kernel.org> >
