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NOTES: Update the HZ entry with latest advice.

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Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D30804
This commit is contained in:
Warner Losh 2021-06-18 08:39:18 -06:00
parent fcf2227a55
commit 0f882bb14a
1 changed files with 6 additions and 10 deletions
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sys/conf/NOTES
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@ -1047,8 +1047,7 @@ options TCP_SIGNATURE #include support for RFC 2385
# DUMMYNET enables the "dummynet" bandwidth limiter. You need IPFIREWALL
# as well. See dummynet(4) and ipfw(8) for more info. When you run
# DUMMYNET it is advisable to also have at least "options HZ=1000" to achieve
# a smooth scheduling of the traffic.
# DUMMYNET, HZ/kern.hz should be at least 1000 for adequate response.
options DUMMYNET
# The DEBUGNET option enables a basic debug/panic-time networking API. It
@ -1237,14 +1236,11 @@ options CAPABILITY_MODE # sandboxes with no global namespace access
#####################################################################
# CLOCK OPTIONS
# The granularity of operation is controlled by the kernel option HZ whose
# default value (1000 on most architectures) means a granularity of 1ms
# (1s/HZ). Historically, the default was 100, but finer granularity is
# required for DUMMYNET and other systems on modern hardware. There are
# reasonable arguments that HZ should, in fact, be 100 still; consider,
# that reducing the granularity too much might cause excessive overhead in
# clock interrupt processing, potentially causing ticks to be missed and thus
# actually reducing the accuracy of operation.
# The granularity of operation is controlled by the kernel option HZ (default
# 1000 or 1ms). Virtual machines guests default to an HZ value of 100. Lower
# values produce less overhead at the expense of reduce accuracy in delivery of
# kernel timeouts. With the adaptive tick code, lower values produce less
# benefit than in the past.
options HZ=100