linux/kernel/sched/debug.c, branch v6.0

sched/debug: fix dentry leak in update_sched_domain_debugfs

2022-09-05T11:02:38Z

Kuyo reports that the pattern of using debugfs_remove(debugfs_lookup()) leaks a dentry and with a hotplug stress test, the machine eventually runs out of memory. Fix this up by using the newly created debugfs_lookup_and_remove() call instead which properly handles the dentry reference counting logic. Cc: Major Chen Cc: stable Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: Valentin Schneider Cc: Matthias Brugger Reported-by: Kuyo Chang Tested-by: Kuyo Chang Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220902123107.109274-2-gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman

sched/headers: Introduce kernel/sched/build_utility.c and build multiple .c files there

2022-02-23T09:58:33Z

Collect all utility functionality source code files into a single kernel/sched/build_utility.c file, via #include-ing the .c files: kernel/sched/clock.c kernel/sched/completion.c kernel/sched/loadavg.c kernel/sched/swait.c kernel/sched/wait_bit.c kernel/sched/wait.c CONFIG_CPU_FREQ: kernel/sched/cpufreq.c CONFIG_CPU_FREQ_GOV_SCHEDUTIL: kernel/sched/cpufreq_schedutil.c CONFIG_CGROUP_CPUACCT: kernel/sched/cpuacct.c CONFIG_SCHED_DEBUG: kernel/sched/debug.c CONFIG_SCHEDSTATS: kernel/sched/stats.c CONFIG_SMP: kernel/sched/cpupri.c kernel/sched/stop_task.c kernel/sched/topology.c CONFIG_SCHED_CORE: kernel/sched/core_sched.c CONFIG_PSI: kernel/sched/psi.c CONFIG_MEMBARRIER: kernel/sched/membarrier.c CONFIG_CPU_ISOLATION: kernel/sched/isolation.c CONFIG_SCHED_AUTOGROUP: kernel/sched/autogroup.c The goal is to amortize the 60+ KLOC header bloat from over a dozen build units into a single build unit. The build time of build_utility.c also roughly matches the build time of core.c and fair.c - allowing better load-balancing of scheduler-only rebuilds. Signed-off-by: Ingo Molnar Reviewed-by: Peter Zijlstra

sched/debug: Remove mpol_get/put and task_lock/unlock from sched_show_numa

2022-01-27T11:57:18Z

The older format of /proc/pid/sched printed home node info which required the mempolicy and task lock around mpol_get(). However the format has changed since then and there is no need for sched_show_numa() any more to have mempolicy argument, asssociated mpol_get/put and task_lock/unlock. Remove them. Fixes: 397f2378f1361 ("sched/numa: Fix numa balancing stats in /proc/pid/sched") Signed-off-by: Bharata B Rao Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Srikar Dronamraju Acked-by: Mel Gorman Link: https://lore.kernel.org/r/20220118050515.2973-1-bharata@amd.com

sched/core: Forced idle accounting

2021-11-17T13:49:00Z

Adds accounting for "forced idle" time, which is time where a cookie'd task forces its SMT sibling to idle, despite the presence of runnable tasks. Forced idle time is one means to measure the cost of enabling core scheduling (ie. the capacity lost due to the need to force idle). Forced idle time is attributed to the thread responsible for causing the forced idle. A few details: - Forced idle time is displayed via /proc/PID/sched. It also requires that schedstats is enabled. - Forced idle is only accounted when a sibling hyperthread is held idle despite the presence of runnable tasks. No time is charged if a sibling is idle but has no runnable tasks. - Tasks with 0 cookie are never charged forced idle. - For SMT > 2, we scale the amount of forced idle charged based on the number of forced idle siblings. Additionally, we split the time up and evenly charge it to all running tasks, as each is equally responsible for the forced idle. Signed-off-by: Josh Don Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20211018203428.2025792-1-joshdon@google.com

sched: Fix DEBUG && !SCHEDSTATS warn

2021-10-06T08:30:57Z

When !SCHEDSTATS schedstat_enabled() is an unconditional 0 and the whole block doesn't exist, however GCC figures the scoped variable 'stats' is unused and complains about it. Upgrade the warning from -Wunused-variable to -Wunused-but-set-variable by writing it in two statements. This fixes the build because the new warning is in W=1. Given that whole if(0) {} thing, I don't feel motivated to change things overly much and quite strongly feel this is the compiler being daft. Fixes: cb3e971c435d ("sched: Make struct sched_statistics independent of fair sched class") Reported-by: Stephen Rothwell Signed-off-by: Peter Zijlstra (Intel)

sched: Introduce task block time in schedstats

2021-10-05T13:51:48Z

Currently in schedstats we have sum_sleep_runtime and iowait_sum, but there's no metric to show how long the task is in D state. Once a task in D state, it means the task is blocked in the kernel, for example the task may be waiting for a mutex. The D state is more frequent than iowait, and it is more critital than S state. So it is worth to add a metric to measure it. Signed-off-by: Yafang Shao Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20210905143547.4668-5-laoar.shao@gmail.com

sched: Make struct sched_statistics independent of fair sched class

2021-10-05T13:51:45Z

If we want to use the schedstats facility to trace other sched classes, we should make it independent of fair sched class. The struct sched_statistics is the schedular statistics of a task_struct or a task_group. So we can move it into struct task_struct and struct task_group to achieve the goal. After the patch, schestats are orgnized as follows, struct task_struct { ... struct sched_entity se; struct sched_rt_entity rt; struct sched_dl_entity dl; ... struct sched_statistics stats; ... }; Regarding the task group, schedstats is only supported for fair group sched, and a new struct sched_entity_stats is introduced, suggested by Peter - struct sched_entity_stats { struct sched_entity se; struct sched_statistics stats; } __no_randomize_layout; Then with the se in a task_group, we can easily get the stats. The sched_statistics members may be frequently modified when schedstats is enabled, in order to avoid impacting on random data which may in the same cacheline with them, the struct sched_statistics is defined as cacheline aligned. As this patch changes the core struct of scheduler, so I verified the performance it may impact on the scheduler with 'perf bench sched pipe', suggested by Mel. Below is the result, in which all the values are in usecs/op. Before After kernel.sched_schedstats=0 5.2~5.4 5.2~5.4 kernel.sched_schedstats=1 5.3~5.5 5.3~5.5 [These data is a little difference with the earlier version, that is because my old test machine is destroyed so I have to use a new different test machine.] Almost no impact on the sched performance. No functional change. [lkp@intel.com: reported build failure in earlier version] Signed-off-by: Yafang Shao Signed-off-by: Peter Zijlstra (Intel) Acked-by: Mel Gorman Link: https://lore.kernel.org/r/20210905143547.4668-3-laoar.shao@gmail.com

sched: reduce sched slice for SCHED_IDLE entities

2021-10-05T13:51:37Z

Use a small, non-scaled min granularity for SCHED_IDLE entities, when competing with normal entities. This reduces the latency of getting a normal entity back on cpu, at the expense of increased context switch frequency of SCHED_IDLE entities. The benefit of this change is to reduce the round-robin latency for normal entities when competing with a SCHED_IDLE entity. Example: on a machine with HZ=1000, spawned two threads, one of which is SCHED_IDLE, and affined to one cpu. Without this patch, the SCHED_IDLE thread runs for 4ms then waits for 1.4s. With this patch, it runs for 1ms and waits 340ms (as it round-robins with the other thread). Signed-off-by: Josh Don Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/20210820010403.946838-4-joshdon@google.com

sched: Account number of SCHED_IDLE entities on each cfs_rq

2021-10-05T13:51:36Z

Adds cfs_rq->idle_nr_running, which accounts the number of idle entities directly enqueued on the cfs_rq. Signed-off-by: Josh Don Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/20210820010403.946838-3-joshdon@google.com

sched/fair: Null terminate buffer when updating tunable_scaling

2021-10-01T11:57:57Z

This patch null-terminates the temporary buffer in sched_scaling_write() so kstrtouint() does not return failure and checks the value is valid. Before: $ cat /sys/kernel/debug/sched/tunable_scaling 1 $ echo 0 > /sys/kernel/debug/sched/tunable_scaling -bash: echo: write error: Invalid argument $ cat /sys/kernel/debug/sched/tunable_scaling 1 After: $ cat /sys/kernel/debug/sched/tunable_scaling 1 $ echo 0 > /sys/kernel/debug/sched/tunable_scaling $ cat /sys/kernel/debug/sched/tunable_scaling 0 $ echo 3 > /sys/kernel/debug/sched/tunable_scaling -bash: echo: write error: Invalid argument Fixes: 8a99b6833c88 ("sched: Move SCHED_DEBUG sysctl to debugfs") Signed-off-by: Mel Gorman Signed-off-by: Peter Zijlstra (Intel) Acked-by: Vincent Guittot Link: https://lore.kernel.org/r/20210927114635.GH3959@techsingularity.net