spinlock vs mutex

found this info nice. noting it.

http://stackoverflow.com/questions/5869825/when-should-one-use-a-spinlock-instead-of-mutex

"In homogeneous multi-core environments, if the time spend on critical section is small than use Spinlock, because we can reduce the context switch time. (Single-core comparison is not important, because some systems implementation Spinlock in the middle of the switch"

is what i took away from it. 

CBR over TCP

here is one study of trying to achieve a CBR over TCP:
http://www.cs.columbia.edu/~salman/publications/votcp-conext07.pdf


two scenarios:
(1) Let's assume that an encoder is generating X bytes/second - and this rate is constant at every time instant (howsoever small a time window we assume).
The goal is to send over these X bytes at Xbytes/second on the network. We would like to  send X bytes/second using TCP, i.e. the instantaneous rate should be X bytes/sec.

We know that TCP's window is chosen to be min(receiver's flow control window, congestion control window (cwnd)), and if we want to have true CBR, we would like to send exactly same number of bytes per second till we experience a loss, and in case of loss somehow compensate for the multiplicative decrease by sending additional data . This is in my opinion pretty hard to achieve.
In other words, it is very hard for instantaneously constant CBR over TCP , however the average behavior over 1 second may be close to CBR.