svn commit: r351918 - head/sys/kern

[Ian Lepore]

On Fri, 2019-09-06 at 01:19 +0000, Philip Paeps wrote:
> Author: philip
> Date: Fri Sep  6 01:19:31 2019
> New Revision: 351918
> URL: https://svnweb.freebsd.org/changeset/base/351918
> 
> Log:
>   riscv: default to HZ=100
>   
>   Most current RISC-V development platforms are not fast enough to
> benefit
>   from the increased granularity provided by HZ=1000.
>   
>   Sponsored by:	Axiado
> 
> Modified:
>   head/sys/kern/subr_param.c
> 
> Modified: head/sys/kern/subr_param.c
> =====================================================================
> =========
> --- head/sys/kern/subr_param.c	Fri Sep  6 00:06:55 2019	(r351
> 917)
> +++ head/sys/kern/subr_param.c	Fri Sep  6 01:19:31 2019	(r351
> 918)
> @@ -61,7 +61,7 @@ __FBSDID("$FreeBSD$");
>   */
>  
>  #ifndef HZ
> -#  if defined(__mips__) || defined(__arm__)
> +#  if defined(__mips__) || defined(__arm__) || defined(__riscv)
>  #    define	HZ 100
>  #  else
>  #    define	HZ 1000
> 

This seems like a bad idea.  I've run a 90mhz armv4 chip with HZ=1000
and didn't notice any performance hit from doing so.  Almost all arm
kernel config files set HZ as an option, so that define doesn't do much
for arm these days.  It probably does still set HZ for various mips
platforms.  

I would think 1000 is appropriate for anything modern running at 200mhz
or more.

Setting it to 100 has the bad side effect of making things like
msleep(), tsleep(), and pause() (which show up in plenty of drivers)
all have a minimum timeout of 10ms, which is a long long time on modern
hardware.

What benefit do you think you'll get from the lower number?

-- Ian