[Drbd-dev] Why sending and receiving dblock is so slow

[Guo, Weiping (Jim)]

Hi DRBD experts,

I did some very basic profiling on drbd. I am really surprised that
sending/receiving could take long time. 

1. sending: I measured the time from a dblock was inserted to the work
queue to when it is actually processed by the worker. Usually it only
takes less than 1ms, but I saw some instances of over 100ms. 

2. receiving: I measured the time to execute read_in_block. I saw some
instances of 80ms and 40ms. Tracking down, it appears that
sock_recvmsg()could take long. 

I just could not understand where those calls are blocked. Is there a
way to speed up the sending/receiving? Any comments and suggestions are
appreciated!

Thank you very much.

Jim