On Sun, Apr 3, 2016 at 7:57 AM, Tom Herbert <t...@herbertland.com> wrote: > I am curious though, how do you think this would specifically help > Android with power? Seems like the receiver still needs to be powered > to receive packets to filter them anyway...
The receiver is powered up, but its wake/sleep cycles are much shorter than the main CPU's. On a phone, leaving the CPU asleep with wifi on might consume ~5mA average, but getting the CPU out of suspend might average ~200mA for ~300ms as the system comes out of sleep, initializes other hardware, wakes up userspace processes whose timeouts have fired, freezes, and suspends again. Receiving one such superfluous packet every 3 seconds (e.g., on networks that send identical IPv6 RAs once every 3 seconds) works out to ~25mA, which is 5x the cost of idle. Pushing down filters to the hardware so it can drop the packet without waking up the CPU thus saves a lot of idle power. That said, getting BPF to the driver is part of the picture. On the chipsets we're targeting for APF, we're only seeing 2k-4k of memory (that's 256-512 BPF instructions) available for filtering code, which means that BPF might be too large.
