What does sbwait mean in top ?
rwatson at FreeBSD.org
Sun Feb 6 16:49:27 PST 2005
On Sun, 6 Feb 2005, Jon Drews wrote:
> What does sbwait mean in top? Is it related to a sysctl setting? I have
> looked in the man page for top, at William LeFebvres site (
> http://www.groupsys.com/top ), in Evi Nemeth's "UNIX System
> Administration Handbook" and Googled in general. Does anyone know of a
> URL that gives an explanation of sbwait and for that matter semwait too.
The sbwait wchan is present when a thread has invoked the in-kernel
sbwait() function to wait for a socket event. It's used in a number of
situations, but the main ones are:
- The thread is trying to send on a blocking socket, but there's
insufficient socket buffer space, so it must wait for space. This might
occur if it has managead to max out the bandwidth available to a TCP
connection, or flow control is in use and the receiver does not wish to
receive more data yet.
- The thread is trying to receive on a blocking socket, but there's not
enough data to satisfy the read request, so it must wait for data to be
received. It might be waiting for a remote TCP sender to have data
available, or for in-flight data to arrive.
Robert N M Watson
More information about the freebsd-questions