Re: Build time measurements

[Andrew Doran <ad%netbsd.org@localhost>]

On Wed, Mar 25, 2020 at 09:44:19PM +0000, Mike Pumford wrote:

> On 24/03/2020 21:47, Andrew Doran wrote:
> > DIAGNOSTIC and acpicpu are disabled in all kernels but they are otherwise
> > GENERIC.  The 2020-04-??  kernel is HEAD plus the remaining changes from the
> > ad-namecache branch.
> > 
> Curious to know why acpicpu is a performance hit. Is it just that it
> downclocks the CPU if you don't have estd to ramp it up or something more
> fundamental?

It's a software problem right now.  The ACPI idle loop doesn't currenly
enter a low power sleep state because there are issues with interrupts to
solve first.  Nevertheless it's very heavy on I/O port access, takes locks
and under certain conditions flushes the entire L1/L2/L3 cache (I haven't
verified that yet but the cache miss rate observed with tprof(8) is very
high).

Andrew