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Brad Fitzpatrick authored
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
e43c2483
