Messages in this thread |  | | Date | Tue, 6 Oct 2020 20:03:22 +0100 | From | Mel Gorman <> | Subject | Re: ACPI _CST introduced performance regresions on Haswll |
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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
-- Mel Gorman SUSE Labs
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