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
