Date: Mon, 7 Feb 2005 00:48:30 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Jon Drews <jon.drews@gmail.com> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: What does sbwait mean in top ? Message-ID: <Pine.NEB.3.96L.1050207004514.61595E-100000@fledge.watson.org> In-Reply-To: <8cb27cbf05020614334a3978cd@mail.gmail.com>
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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
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