We seeing lot of empty requests from nginx process trace. Is this normal or some kind of Dos attack?

0.000048 recvfrom(254, "", 1024, 0, NULL, NULL) = 0
0.000033 close(254) = 0
0.000054 recvfrom(600, "", 1024, 0, NULL, NULL) = 0
0.000029 close(600) = 0
0.000040 recvfrom(147, "", 1024, 0, NULL, NULL) = 0
0.000029 close(147) = 0
0.000066 recvfrom(644, "", 1024, 0, NULL, NULL) = 0
0.000029 close(644) = 0
0.000642 recvfrom(519, "", 1024, 0, NULL, NULL) = 0
0.000040 close(519) = 0
0.000047 recvfrom(361, "", 1024, 0, NULL, NULL) = 0
0.000031 close(361) = 0
0.000047 recvfrom(248, "", 1024, 0, NULL, NULL) = 0
0.000036 close(248) = 0
0.000044 recvfrom(691, "", 1024, 0, NULL, NULL) = 0
0.000029 close(691) = 0
0.000046 recvfrom(561, "", 1024, 0, NULL, NULL) = 0
0.000031 close(561) = 0
0.000046 recvfrom(270, "", 1024, 0, NULL, NULL) = 0
0.000031 close(270) = 0
0.000049 recvfrom(723, "", 1024, 0, NULL, NULL) = 0
0.000030 close(723) = 0
0.000046 recvfrom(362, "", 1024, 0, NULL, NULL) = 0
0.000032 close(362) = 0