On 10/6/2020 9:03 PM, Mel Gorman wrote:
On Tue, Oct 06, 2020 at 06:00:18PM +0200, Rafael J. Wysocki wrote:
server systems") and enable-cst is the commit. It was not fixed by 5.6 or
5.9-rc8. A lot of bisections ended up here including kernel compilation,
tbench, syscall entry/exit microbenchmark, hackbench, Java workloads etc.
What I don't understand is why. The latencies for c-state exit states
before and after the patch are both as follows
/sys/devices/system/cpu/cpu0/cpuidle/state0/latency:0
/sys/devices/system/cpu/cpu0/cpuidle/state1/latency:2
/sys/devices/system/cpu/cpu0/cpuidle/state2/latency:10
/sys/devices/system/cpu/cpu0/cpuidle/state3/latency:33
/sys/devices/system/cpu/cpu0/cpuidle/state4/latency:133
Perf profiles did not show up anything interesting. A diff of
/sys/devices/system/cpu/cpu0/cpuidle/state0/ before and after the patch
showed up nothing interesting. Any idea why exactly this patch shows up
as being hazardous on Haswell in particular?
Presumably, some of the idle states are disabled by default on the affected
machines.
Can you check the disable and default_status attributes of each state before
and after the commit in question?
# grep . pre-cst/cpuidle/state*/disable
pre-cst/cpuidle/state0/disable:0
pre-cst/cpuidle/state1/disable:0
pre-cst/cpuidle/state2/disable:0
pre-cst/cpuidle/state3/disable:0
pre-cst/cpuidle/state4/disable:0
# grep . enable-cst/cpuidle/state*/disable
enable-cst/cpuidle/state0/disable:0
enable-cst/cpuidle/state1/disable:0
enable-cst/cpuidle/state2/disable:0
enable-cst/cpuidle/state3/disable:0
enable-cst/cpuidle/state4/disable:0
# grep . pre-cst/cpuidle/state*/default_status
pre-cst/cpuidle/state0/default_status:enabled
pre-cst/cpuidle/state1/default_status:enabled
pre-cst/cpuidle/state2/default_status:enabled
pre-cst/cpuidle/state3/default_status:enabled
pre-cst/cpuidle/state4/default_status:enabled
After the commit, the default_status file does not appear in /sys
Something is amiss, then, because the commit doesn't affect the presence
of this file.
The only thing it does is to set the use_acpi flag for several processor
models in intel_idle.c.
It can be effectively reversed by removing all of the ".use_acpi =
true," lines from intel_idle.c.
In particular, please check if changing the value of use_acpi in struct
idle_cpu_hsx from 'true' to 'false' alone (without reverting the commit)
makes the issue go away in 5.9-rc8 (the default_status file should be
present regardless).
Cheers!
