svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
h_ertt(4)
The Khelp module works within the framework to provide TCP with a
per-connection, low noise estimate of the instantaneous RTT. The
implementation attempts to be robust in the face of delayed ac‐
knowledgements, TCP Segmentation Offload (TSO), receivers who ma‐
nipulate TCP timestamps and lack of the TCP timestamp option al‐
together. TCP receivers using delayed acknowledgements either
acknowledge every second packet (reflecting the time stamp of the
first) or use a timeout to trigger the acknowledgement if no sec‐
ond packet arrives. If the heuristic used by determines that the
receiver is using delayed acknowledgements, it measures the RTT
using the second packet (the one that triggers the acknowledge‐
ment). It does not measure the RTT if the acknowledgement is for
the first packet, since it cannot be accurately determined. When
TSO is in use, will momentarily disable TSO whilst marking a
packet to use for a new measurement. The process has negligible
impact on the connection. associates the following struct with
each connection's TCP control block: struct ertt {
TAILQ_HEAD(txseginfo_head, txseginfo) txsegi_q; /* Pri‐
vate. */
long bytes_tx_in_rtt; /* Pri‐
vate. */ long bytes_tx_in_marked_rtt;
unsigned long marked_snd_cwnd;
int rtt; int maxrtt;
int minrtt; int dly‐
ack_rx; /* Private. */
int timestamp_errors; /* Pri‐
vate. */
int markedpkt_rtt; /* Pri‐
vate. */ uint32_t flags; }; The fields marked as
private should not be manipulated by any code outside of the im‐
plementation. The non-private fields provide the following data:
The number of bytes transmitted in the The value of cwnd for the
marked rtt measurement. The most recent RTT measurement. The
longest RTT measurement that has been taken. The shortest RTT
measurement that has been taken. The ERTT_NEW_MEASUREMENT flag
will be set by the implementation when a new measurement is
available. It is the responsibility of consumers to unset the
flag if they wish to use it as a notification method for new mea‐
surements. Development and testing of this software were made
possible in part by grants from the FreeBSD Foundation and Cisco
University Research Program Fund at Community Foundation Silicon
Valley. The module first appeared in The module was first re‐
leased in 2010 by David Hayes whilst working on the NewTCP re‐
search project at Swinburne University of Technology's Centre for
Advanced Internet Architectures, Melbourne, Australia. More de‐
tails are available at: http://caia.swin.edu.au/urp/newtcp/ The
Khelp module and this manual page were written by The module
maintains enhanced RTT estimates for all new TCP connections cre‐
ated after the time at which the module was loaded. It might be
beneficial to see if it is possible to have the module only af‐
fect connections which actually care about ERTT estimates.