More fixes to Binder perf regression from Eclair
Re-use the file descriptor to change the cgroups. There's a fast path
in the kernel for the case where the value's already uncahnged. Also,
this is okay because the kernel ignores the write offset. This is
essentially a ioctl-ish/datagram interface, despite being a fd we're
writing to.
This reduces Dalvik->Dalvik void/void Binder calls on Sapphire from
~1.2 to ~0.8 ms. This is a bit slower than the ~0.7 ms we get
avoiding the write altogether.
strace confirms:
[pid 1557] ioctl(21, 0xc0186201 <unfinished ...>
[pid 1556] <... ioctl resumed> , 0x45399cd0) = 0
[pid 1556] write(22, "1556", 4) = 4
[pid 1556] ioctl(21, 0xc0186201 <unfinished ...>
[pid 1555] <... ioctl resumed> , 0x45299cd0) = 0
[pid 1555] write(22, "1555", 4) = 4
[pid 1555] ioctl(21, 0xc0186201 <unfinished ...>
[pid 1554] <... ioctl resumed> , 0x45199cd0) = 0
[pid 1554] write(22, "1554", 4) = 4
BUG=2660235
Change-Id: Ia9f9e1d5b792eaebc9560f89931faf6df0cf9c0d
1 file changed
