git: 0f882bb14a0e - main - NOTES: Update the HZ entry with latest advice.

[Gary Jennejohn]

On Fri, 18 Jun 2021 14:43:48 GMT
Warner Losh <imp at FreeBSD.org> wrote:

> The branch main has been updated by imp:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=0f882bb14a0e772bf901b1a3e40d028a4165fbd9
> 
> commit 0f882bb14a0e772bf901b1a3e40d028a4165fbd9
> Author:     Warner Losh <imp at FreeBSD.org>
> AuthorDate: 2021-06-18 14:39:18 +0000
> Commit:     Warner Losh <imp at FreeBSD.org>
> CommitDate: 2021-06-18 14:41:56 +0000
> 
>     NOTES: Update the HZ entry with latest advice.
>     
>     Sponsored by:           Netflix
>     Differential Revision:  https://reviews.freebsd.org/D30804
> ---
>  sys/conf/NOTES | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/sys/conf/NOTES b/sys/conf/NOTES
> index 40063c09382f..89dd572986bc 100644
> --- a/sys/conf/NOTES
> +++ b/sys/conf/NOTES
> @@ -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

reduce should be reduced

> +# kernel timeouts. With the adaptive tick code, lower values produce less
> +# benefit than in the past.
>  
>  options 	HZ=100
>  
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-- 
Gary Jennejohn