Hi , In my embedded linux-arm target , in a userspace thread , i am reading hid events over usb-hiddev interface (/dev/hiddev) . basically what i do is this : read_thread(){ while(1){ ret = read( "/dev/hiddev" , user_buffer , bytes_to_read); printf("bytes received =%d" , ret ) ; // (printf prints debug message to serial console ); } } now whenever i use the printf statement in read thread , kernel space ring buffer in usb-hid driver is overrun frequently , which results in loss of data send by usb device . if i remove printf in read thread , no overruns are reported in usb-hid driver . that means if printf is used , application read_thread is not able to read data in time which leads to driver ring buffer overrun . does this behaviour of printf points to some problem in embedded linux's scheduler ( printf prints data to debug serial port , and consecutive read() calls in read_thread() are scheduled lately due to that ) ? do the actual implementation of printf involves any kind of sleeps ? kindly share necessary insight wrt above printf usage and driver ring buffer overrun . regards Amit Nagal