Hi Doug,
On 20/03/21 8:34 pm, Doug Smythies wrote:
On Wed, Mar 17, 2021 at 11:44 PM Pratik Sampat psampat@linux.ibm.com wrote:
Hi Doug, Thanks for trying these patches out.
On 18/03/21 2:30 am, Doug Smythies wrote:
Hi Pratik,
It just so happens that I have been trying Artem's version this last week, so I tried yours.
On Mon, Mar 15, 2021 at 4:49 AM Pratik Rajesh Sampat psampat@linux.ibm.com wrote: ...
...
Other notes:
No idle state for CPU 0 ever gets disabled. I assume this is because CPU 0 can never be offline, so that bit of code (Disable all stop states) doesn't find its state. By the way, processor = Intel i5-9600K
I had tried these patches on an IBM POWER 9 processor and disabling CPU0's idle state works there. However, it does make sense for some processors to treat CPU 0 differently. Maybe I could write in a case if idle state disabling fails for a CPU then we just skip it?
I didn't try it, I just did a hack so I could continue for this reply.
Sure. In subsequent version I could write something to cleanly handle online fail checks, maybe even specifically for CPU0.
The system is left with all idle states disabled, well not for CPU 0 as per the above comment. The suggestion is to restore them, otherwise my processor hogs 42 watts instead of 2.
My results are highly variable per test.
Question: Do you notice high variability with IPI test, Timer test or both?
The IPI test has less variability than the Timer test.
I can think of two reasons for high run to run variance:
- If you observe variance in timer tests, then I believe there could a
mechanism of "C-state pre-wake" on some Intel machines at play here, which can pre-wake a CPU from an idle state when timers are armed. I'm not sure if the Intel platform that you're running on does that or not.
Artem had described this behavior to me a while ago and I think his wult page describes this behavior in more detail: https://intel.github.io/wult/#c-state-pre-wake
Yes, I have reviewed all the references. And yes, I think my processors have the pre-wake stuff.
I do not have the proper hardware to do the Artem pre-wake workaround method, but might buy it in future.
That explains the variability that we are seeing in the Timer tests on the Intel processor you've tried on. Also based on the data pasted below, it means that the IPI tests are more reliable than Timers.
Maybe it would be better to not run the Timer test on Intel platforms that support this pre-wakeup feature? However, I don't know how (or if) Intel exposes this information to the userspace and if other platforms like AMD also have this feature in some form.
Another way of solving this problem could be to have the timer test as an optional parameter in the selftest for people to use while also printing a disclaimer for x86 users about the potential hardware design?
-- Thanks Pratik
- I have noticed variability in results when there are kernel book-keeping or
jitter tasks scheduled from time to time on an otherwise idle core. In the full per-CPU logs at tools/testing/selftests/cpuidle/cpuidle.log can you spot any obvious outliers per-CPU state?
Yes. I'll just paste in an example cpuidle.log file having used the -v option below, along with my hack job diff.
doug@s19:~/temp-k-git/linux/tools/testing/selftests/cpuidle$ cat cpuidle.log.v3-1 --IPI Latency Test--- --Baseline IPI Latency measurement: CPU Busy-- SRC_CPU DEST_CPU IPI_Latency(ns) 0 0 140 0 1 632 0 2 675 0 3 671 0 4 675 0 5 767 0 6 653 0 7 826 0 8 819 0 9 615 0 10 758 0 11 758 Baseline Avg IPI latency(ns): 665 ---Enabling state: 0--- SRC_CPU DEST_CPU IPI_Latency(ns) 0 0 76 0 1 484 0 2 494 0 3 539 0 4 498 0 5 491 0 6 474 0 7 434 0 8 544 0 9 476 0 10 447 0 11 467 Expected IPI latency(ns): 0 Observed Avg IPI latency(ns) - State 0: 452 ---Enabling state: 1--- SRC_CPU DEST_CPU IPI_Latency(ns) 0 0 72 0 1 1081 0 2 821 0 3 1486 0 4 1022 0 5 960 0 6 1634 0 7 933 0 8 1032 0 9 1046 0 10 1430 0 11 1338 Expected IPI latency(ns): 1000 Observed Avg IPI latency(ns) - State 1: 1071 ---Enabling state: 2--- SRC_CPU DEST_CPU IPI_Latency(ns) 0 0 264 0 1 30836 0 2 30562 0 3 30748 0 4 35286 0 5 30978 0 6 1952 0 7 36066 0 8 30670 0 9 30605 0 10 30635 0 11 35423 Expected IPI latency(ns): 120000 Observed Avg IPI latency(ns) - State 2: 27002 ---Enabling state: 3--- SRC_CPU DEST_CPU IPI_Latency(ns) 0 0 71 0 1 30853 0 2 32095 0 3 32661 0 4 30230 0 5 34348 0 6 2012 0 7 30816 0 8 30908 0 9 31130 0 10 34150 0 11 32050 Expected IPI latency(ns): 1034000 Observed Avg IPI latency(ns) - State 3: 26777
--Timeout Latency Test-- --Baseline Timeout Latency measurement: CPU Busy-- Wakeup_src Baseline_delay(ns) 0 453 1 568 2 387 3 337 4 433 5 579 6 330 7 400 8 561 9 544 10 569 11 523 Baseline Avg timeout diff(ns): 473 ---Enabling state: 0--- Wakeup_src Baseline_delay(ns) Delay(ns) 0 399 1 388 2 352 3 385 4 334 5 415 6 320 7 356 8 401 9 379 10 339 11 384 Expected timeout(ns): 200 Observed Avg timeout diff(ns) - State 0: 371 ---Enabling state: 1--- Wakeup_src Baseline_delay(ns) Delay(ns) 0 666 1 575 2 608 3 590 4 608 5 552 6 582 7 593 8 597 9 587 10 588 11 610 Expected timeout(ns): 1200 Observed Avg timeout diff(ns) - State 1: 596 ---Enabling state: 2--- Wakeup_src Baseline_delay(ns) Delay(ns) 0 36386 1 1069 2 866 3 884 4 850 5 55642 6 408082 7 1184 8 406075 9 406830 10 414105 11 406594 Expected timeout(ns): 360200 Observed Avg timeout diff(ns) - State 2: 178213 ---Enabling state: 3--- Wakeup_src Baseline_delay(ns) Delay(ns) 0 406049 1 913 2 410134 3 921 4 406237 5 950 6 407181 7 920 8 407678 9 894 10 406320 11 304161 Expected timeout(ns): 3102200 Observed Avg timeout diff(ns) - State 3: 229363
My hack job, (CPUs always online):
diff --git a/tools/testing/selftests/cpuidle/cpuidle.sh b/tools/testing/selftests/cpuidle/cpuidle.sh index de5141d5b76b..70bdacda5e91 100755 --- a/tools/testing/selftests/cpuidle/cpuidle.sh +++ b/tools/testing/selftests/cpuidle/cpuidle.sh @@ -86,10 +86,6 @@ disable_idle() { for ((cpu=0; cpu<NUM_CPUS; cpu++)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi for ((state=0; state<NUM_STATES; state++)) do echo 1 >/sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable @@ -104,10 +100,6 @@ op_state() { for ((cpu=0; cpu<NUM_CPUS; cpu++)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi echo $1 >/sys/devices/system/cpu/cpu$cpu/cpuidle/state$2/disable done } @@ -124,17 +116,6 @@ cpuidle_disable_state() op_state 1 $state }
-cpu_is_online() -{
cpu=$1if [ ! -f "/sys/devices/system/cpu/cpu$cpu/online" ]; thenecho 0returnfistatus=$(cat /sys/devices/system/cpu/cpu$cpu/online)echo $status-}
- # Extract latency in microseconds and convert to nanoseconds extract_latency() {
@@ -179,10 +160,6 @@ run_ipi_tests() printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >> $LOG for ((cpu=0; cpu<NUM_CPUS; cpu+=SMT)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi ipi_test_once "baseline" $cpu printf "%-3s %10s %12s\n" $src_cpu $cpu $ipi_latency >> $LOG avg_arr+=($ipi_latency)@@ -198,10 +175,6 @@ run_ipi_tests() printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >> $LOG for ((cpu=0; cpu<NUM_CPUS; cpu+=SMT)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi # Running IPI test and logging results sleep 1 ipi_test_once "test" $cpu@@ -262,10 +235,6 @@ run_timeout_tests() printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)">> $LOG for ((cpu=0; cpu<NUM_CPUS; cpu+=SMT)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi timeout_test_once "baseline" $cpu 1000000 printf "%-3s %13s\n" $src_cpu $timeout_diff >> $LOG avg_arr+=($timeout_diff)@@ -281,10 +250,6 @@ run_timeout_tests() printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)" "Delay(ns)" >> $LOG for ((cpu=0; cpu<NUM_CPUS; cpu+=SMT)) do
local cpu_status=$(cpu_is_online $cpu)if [ $cpu_status == 0 ]; thencontinuefi timeout_test_once "test" $cpu 1000000 printf "%-3s %13s %18s\n" $src_cpu$baseline_timeout_diff $timeout_diff >> $LOG avg_arr+=($timeout_diff) @@ -314,3 +279,7 @@ run_timeout_tests printf "Removing $MODULE module\n" printf "Full Output logged at: $LOG\n" rmmod $MODULE
+printf "enabling idle states\n"
+echo 0 | tee /sys/devices/system/cpu/cpu*/cpuidle/state*/disable (END)