When I log into gnome-wayland from gdm in F22 (both on hardware or in VM), then top shows that process gnome-shell --mode=gdm takes relatively big portion of CPU time (while should be rather inactive). Strace reveals that the process runs this syscalls in a loop:

recvmsg(43, 0x7fff5bf946a0, 0)          = -1 EAGAIN
poll([{fd=4, events=POLLIN}, ..., 14, 98) = 0 (Timeout)
recvmsg(43, 0x7fff5bf946a0, 0)          = -1 EAGAIN 
poll([{fd=4, events=POLLIN}, ..., 14, 0) = 0 (Timeout)
open("/proc/self/stat", O_RDONLY)       = 12
fstat(12, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
fcntl(12, F_GETFL)                      = 0x8000 (flags O_RDONLY|O_LARGEFILE)
fstat(12, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fcc0c623000
read(12, "1334 (gnome-shell) R 1318 1312 1"..., 4096) = 351
read(12, "", 3072)                      = 0
close(12)                               = 0
munmap(0x7fcc0c623000, 4096)            = 0

The poll called from g_main_loop from meta_run() and the recvmsg's callstack is:

+ Trace 234980