kernel.git/drivers/cpuidle, branch linux-6.12.y

cpuidle: Skip governor when only one idle state is available

2026-03-04T12:20:35Z

[ Upstream commit e5c9ffc6ae1bcdb1062527d611043681ac301aca ] On certain platforms (PowerNV systems without a power-mgt DT node), cpuidle may register only a single idle state. In cases where that single state is a polling state (state 0), the ladder governor may incorrectly treat state 1 as the first usable state and pass an out-of-bounds index. This can lead to a NULL enter callback being invoked, ultimately resulting in a system crash. [ 13.342636] cpuidle-powernv : Only Snooze is available [ 13.351854] Faulting instruction address: 0x00000000 [ 13.376489] NIP [0000000000000000] 0x0 [ 13.378351] LR [c000000001e01974] cpuidle_enter_state+0x2c4/0x668 Fix this by adding a bail-out in cpuidle_select() that returns state 0 directly when state_count <= 1, bypassing the governor and keeping the tick running. Fixes: dc2251bf98c6 ("cpuidle: Eliminate the CPUIDLE_DRIVER_STATE_START symbol") Signed-off-by: Aboorva Devarajan Reviewed-by: Christian Loehle Link: https://patch.msgid.link/20260216185005.1131593-2-aboorvad@linux.ibm.com Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

cpuidle: governors: menu: Always check timers with tick stopped

2026-03-04T12:19:28Z

[ Upstream commit 80606f4eb8d7484ab7f7d6f0fd30d71e6fbcf328 ] After commit 5484e31bbbff ("cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases"), if the return value of get_typical_interval() multiplied by NSEC_PER_USEC is not greater than RESIDENCY_THRESHOLD_NS, the menu governor will skip computing the time till the closest timer. If that happens when the tick has been stopped already, the selected idle state may be too deep due to the subsequent check comparing predicted_ns with TICK_NSEC and causing its value to be replaced with the expected time till the closest timer, which is KTIME_MAX in that case. That will cause the deepest enabled idle state to be selected, but the time till the closest timer very well may be shorter than the target residency of that state, in which case a shallower state should be used. Address this by making menu_select() always compute the time till the closest timer when the tick has been stopped. Also move the predicted_ns check mentioned above into the branch in which the time till the closest timer is determined because it only needs to be done in that case. Fixes: 5484e31bbbff ("cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases") Signed-off-by: Rafael J. Wysocki Reviewed-by: Christian Loehle Link: https://patch.msgid.link/5959091.DvuYhMxLoT@rafael.j.wysocki Signed-off-by: Sasha Levin

cpuidle: governors: teo: Drop misguided target residency check

2026-01-08T09:14:19Z

commit a03b2011808ab02ccb7ab6b573b013b77fbb5921 upstream. When the target residency of the current candidate idle state is greater than the expected time till the closest timer (the sleep length), it does not matter whether or not the tick has already been stopped or if it is going to be stopped. The closest timer will trigger anyway at its due time, so if an idle state with target residency above the sleep length is selected, energy will be wasted and there may be excess latency. Of course, if the closest timer were canceled before it could trigger, a deeper idle state would be more suitable, but this is not expected to happen (generally speaking, hrtimers are not expected to be canceled as a rule). Accordingly, the teo_state_ok() check done in that case causes energy to be wasted more often than it allows any energy to be saved (if it allows any energy to be saved at all), so drop it and let the governor use the teo_find_shallower_state() return value as the new candidate idle state index. Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront") Cc: All applicable Signed-off-by: Rafael J. Wysocki Reviewed-by: Christian Loehle Tested-by: Christian Loehle Link: https://patch.msgid.link/5955081.DvuYhMxLoT@rafael.j.wysocki Signed-off-by: Greg Kroah-Hartman

cpuidle: menu: Use residency threshold in polling state override decisions

2026-01-08T09:13:56Z

[ Upstream commit 07d815701274d156ad8c7c088a52e01642156fb8 ] On virtualized PowerPC (pseries) systems, where only one polling state (Snooze) and one deep state (CEDE) are available, selecting CEDE when the predicted idle duration is less than the target residency of CEDE state can hurt performance. In such cases, the entry/exit overhead of CEDE outweighs the power savings, leading to unnecessary state transitions and higher latency. Menu governor currently contains a special-case rule that prioritizes the first non-polling state over polling, even when its target residency is much longer than the predicted idle duration. On PowerPC/pseries, where the gap between the polling state (Snooze) and the first non-polling state (CEDE) is large, this behavior causes performance regressions. Refine that special case by adding an extra requirement: the first non-polling state can only be chosen if its target residency is below the defined RESIDENCY_THRESHOLD_NS. If this condition is not satisfied, polling is allowed instead, avoiding suboptimal non-polling state entries. This change is limited to the single special-case rule for the first non-polling state. The general non-polling state selection logic in the menu governor remains unchanged. Performance improvement observed with pgbench on PowerPC (pseries) system: +---------------------------+------------+------------+------------+ | Metric | Baseline | Patched | Change (%) | +---------------------------+------------+------------+------------+ | Transactions/sec (TPS) | 495,210 | 536,982 | +8.45% | | Avg latency (ms) | 0.163 | 0.150 | -7.98% | +---------------------------+------------+------------+------------+ CPUIdle state usage: +--------------+--------------+-------------+ | Metric | Baseline | Patched | +--------------+--------------+-------------+ | Total usage | 12,735,820 | 13,918,442 | | Above usage | 11,401,520 | 1,598,210 | | Below usage | 20,145 | 702,395 | +--------------+--------------+-------------+ Above/Total and Below/Total usage percentages: +------------------------+-----------+---------+ | Metric | Baseline | Patched | +------------------------+-----------+---------+ | Above % (Above/Total) | 89.56% | 11.49% | | Below % (Below/Total) | 0.16% | 5.05% | | Total cpuidle miss (%) | 89.72% | 16.54% | +------------------------+-----------+---------+ The results indicate that restricting CEDE selection to cases where its residency matches the predicted idle time reduces mispredictions, lowers unnecessary state transitions, and improves overall throughput. Reviewed-by: Christian Loehle Signed-off-by: Aboorva Devarajan [ rjw: Changelog edits, rebase ] Link: https://patch.msgid.link/20251006013954.17972-1-aboorvad@linux.ibm.com Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

cpuidle: Fail cpuidle device registration if there is one already

2025-11-13T20:34:06Z

[ Upstream commit 7b1b7961170e4fcad488755e5ffaaaf9bd527e8f ] Refuse to register a cpuidle device if the given CPU has a cpuidle device already and print a message regarding it. Without this, an attempt to register a new cpuidle device without unregistering the existing one leads to the removal of the existing cpuidle device without removing its sysfs interface. Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

cpuidle: governors: menu: Select polling state in some more cases

2025-11-13T20:34:01Z

[ Upstream commit db86f55bf81a3a297be05ee8775ae9a8c6e3a599 ] A throughput regression of 11% introduced by commit 779b1a1cb13a ("cpuidle: governors: menu: Avoid selecting states with too much latency") has been reported and it is related to the case when the menu governor checks if selecting a proper idle state instead of a polling one makes sense. In particular, it is questionable to do so if the exit latency of the idle state in question exceeds the predicted idle duration, so add a check for that, which is sufficient to make the reported regression go away, and update the related code comment accordingly. Fixes: 779b1a1cb13a ("cpuidle: governors: menu: Avoid selecting states with too much latency") Closes: https://lore.kernel.org/linux-pm/004501dc43c9$ec8aa930$c59ffb90$@telus.net/ Reported-by: Doug Smythies Tested-by: Doug Smythies Cc: All applicable Signed-off-by: Rafael J. Wysocki Reviewed-by: Christian Loehle Link: https://patch.msgid.link/12786727.O9o76ZdvQC@rafael.j.wysocki Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

cpuidle: governors: menu: Rearrange main loop in menu_select()

2025-11-13T20:34:01Z

[ Upstream commit 17224c1d2574d29668c4879e1fbf36d6f68cd22b ] Reduce the indentation level in the main loop of menu_select() by rearranging some checks and assignments in it. No intentional functional impact. Signed-off-by: Rafael J. Wysocki Reviewed-by: Christian Loehle Link: https://patch.msgid.link/2389215.ElGaqSPkdT@rafael.j.wysocki Stable-dep-of: db86f55bf81a ("cpuidle: governors: menu: Select polling state in some more cases") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

Revert "cpuidle: menu: Avoid discarding useful information"

2025-10-29T13:08:56Z

commit 10fad4012234a7dea621ae17c0c9486824f645a0 upstream. It is reported that commit 85975daeaa4d ("cpuidle: menu: Avoid discarding useful information") led to a performance regression on Intel Jasper Lake systems because it reduced the time spent by CPUs in idle state C7 which is correlated to the maximum frequency the CPUs can get to because of an average running power limit [1]. Before that commit, get_typical_interval() would have returned UINT_MAX whenever it had been unable to make a high-confidence prediction which had led to selecting the deepest available idle state too often and both power and performance had been inadequate as a result of that on some systems. However, this had not been a problem on systems with relatively aggressive average running power limits, like the Jasper Lake systems in question, because on those systems it was compensated by the ability to run CPUs faster. It was addressed by causing get_typical_interval() to return a number based on the recent idle duration information available to it even if it could not make a high-confidence prediction, but that clearly did not take the possible correlation between idle power and available CPU capacity into account. For this reason, revert most of the changes made by commit 85975daeaa4d, except for one cosmetic cleanup, and add a comment explaining the rationale for returning UINT_MAX from get_typical_interval() when it is unable to make a high-confidence prediction. Fixes: 85975daeaa4d ("cpuidle: menu: Avoid discarding useful information") Closes: https://lore.kernel.org/linux-pm/36iykr223vmcfsoysexug6s274nq2oimcu55ybn6ww4il3g3cv@cohflgdbpnq7/ [1] Reported-by: Sergey Senozhatsky Cc: All applicable Signed-off-by: Rafael J. Wysocki Link: https://patch.msgid.link/3663603.iIbC2pHGDl@rafael.j.wysocki Signed-off-by: Greg Kroah-Hartman

cpuidle: qcom-spm: fix device and OF node leaks at probe

2025-10-15T10:00:00Z

[ Upstream commit cdc06f912670c8c199d5fa9e78b64b7ed8e871d0 ] Make sure to drop the reference to the saw device taken by of_find_device_by_node() after retrieving its driver data during probe(). Also drop the reference to the CPU node sooner to avoid leaking it in case there is no saw node or device. Fixes: 60f3692b5f0b ("cpuidle: qcom_spm: Detach state machine from main SPM handling") Signed-off-by: Johan Hovold Reviewed-by: Konrad Dybcio Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

cpuidle: governors: menu: Avoid selecting states with too much latency

2025-08-28T14:31:08Z

[ Upstream commit 779b1a1cb13ae17028aeddb2fbbdba97357a1e15 ] Occasionally, the exit latency of the idle state selected by the menu governor may exceed the PM QoS CPU wakeup latency limit. Namely, if the scheduler tick has been stopped already and predicted_ns is greater than the tick period length, the governor may return an idle state whose exit latency exceeds latency_req because that decision is made before checking the current idle state's exit latency. For instance, say that there are 3 idle states, 0, 1, and 2. For idle states 0 and 1, the exit latency is equal to the target residency and the values are 0 and 5 us, respectively. State 2 is deeper and has the exit latency and target residency of 200 us and 2 ms (which is greater than the tick period length), respectively. Say that predicted_ns is equal to TICK_NSEC and the PM QoS latency limit is 20 us. After the first two iterations of the main loop in menu_select(), idx becomes 1 and in the third iteration of it the target residency of the current state (state 2) is greater than predicted_ns. State 2 is not a polling one and predicted_ns is not less than TICK_NSEC, so the check on whether or not the tick has been stopped is done. Say that the tick has been stopped already and there are no imminent timers (that is, delta_tick is greater than the target residency of state 2). In that case, idx becomes 2 and it is returned immediately, but the exit latency of state 2 exceeds the latency limit. Address this issue by modifying the code to compare the exit latency of the current idle state (idle state i) with the latency limit before comparing its target residency with predicted_ns, which allows one more exit_latency_ns check that becomes redundant to be dropped. However, after the above change, latency_req cannot take the predicted_ns value any more, which takes place after commit 38f83090f515 ("cpuidle: menu: Remove iowait influence"), because it may cause a polling state to be returned prematurely. In the context of the previous example say that predicted_ns is 3000 and the PM QoS latency limit is still 20 us. Additionally, say that idle state 0 is a polling one. Moving the exit_latency_ns check before the target_residency_ns one causes the loop to terminate in the second iteration, before the target_residency_ns check, so idle state 0 will be returned even though previously state 1 would be returned if there were no imminent timers. For this reason, remove the assignment of the predicted_ns value to latency_req from the code. Fixes: 5ef499cd571c ("cpuidle: menu: Handle stopped tick more aggressively") Cc: 4.17+ # 4.17+ Signed-off-by: Rafael J. Wysocki Reviewed-by: Christian Loehle Link: https://patch.msgid.link/5043159.31r3eYUQgx@rafael.j.wysocki Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman