Messages in this thread |  | | Date | Tue, 6 Oct 2020 20:47:45 +0100 | From | Mel Gorman <> | Subject | Re: ACPI _CST introduced performance regresions on Haswll |
| |
On Tue, Oct 06, 2020 at 08:03:22PM +0100, 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
Sorry, second attempt after thinking the results made no sense at all. Turns out I fat fingered setting up the enable-cst kernel the second time to collect what you asked for and the patch was not applied at all.
# 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 . 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 # 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:1 enable-cst/cpuidle/state4/disable:1 # grep . enable-cst/cpuidle/state*/default_status enable-cst/cpuidle/state0/default_status:enabled enable-cst/cpuidle/state1/default_status:enabled enable-cst/cpuidle/state2/default_status:enabled enable-cst/cpuidle/state3/default_status:disabled enable-cst/cpuidle/state4/default_status:disabled
That looks like C3 and C6 are disabled after the patch.
# grep . enable-cst/cpuidle/state*/name enable-cst/cpuidle/state0/name:POLL enable-cst/cpuidle/state1/name:C1 enable-cst/cpuidle/state2/name:C1E enable-cst/cpuidle/state3/name:C3 enable-cst/cpuidle/state4/name:C6
-- Mel Gorman SUSE Labs
|  |