From b2b00ddf193bf83dc561d965c67b18eb54ebcd83 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 30 Oct 2019 11:56:10 -0700 Subject: rcu: React to callback overload by aggressively seeking quiescent states In default configutions, RCU currently waits at least 100 milliseconds before asking cond_resched() and/or resched_rcu() for help seeking quiescent states to end a grace period. But 100 milliseconds can be one good long time during an RCU callback flood, for example, as can happen when user processes repeatedly open and close files in a tight loop. These 100-millisecond gaps in successive grace periods during a callback flood can result in excessive numbers of callbacks piling up, unnecessarily increasing memory footprint. This commit therefore asks cond_resched() and/or resched_rcu() for help as early as the first FQS scan when at least one of the CPUs has more than 20,000 callbacks queued, a number that can be changed using the new rcutree.qovld kernel boot parameter. An auxiliary qovld_calc variable is used to avoid acquisition of locks that have not yet been initialized. Early tests indicate that this reduces the RCU-callback memory footprint during rcutorture floods by from 50% to 4x, depending on configuration. Reported-by: Joel Fernandes (Google) Reported-by: Tejun Heo [ paulmck: Fix bug located by Qian Cai. ] Signed-off-by: Paul E. McKenney Tested-by: Dexuan Cui Tested-by: Qian Cai --- Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index dbc22d684627..dbd4b4a65209 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3980,6 +3980,15 @@ Set threshold of queued RCU callbacks below which batch limiting is re-enabled. + rcutree.qovld= [KNL] + Set threshold of queued RCU callbacks beyond which + RCU's force-quiescent-state scan will aggressively + enlist help from cond_resched() and sched IPIs to + help CPUs more quickly reach quiescent states. + Set to less than zero to make this be set based + on rcutree.qhimark at boot time and to zero to + disable more aggressive help enlistment. + rcutree.rcu_idle_gp_delay= [KNL] Set wakeup interval for idle CPUs that have RCU callbacks (RCU_FAST_NO_HZ=y). -- cgit v1.2.3 From 58c53360b36d2077cbb843e7ad2bf75f0498271c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 5 Dec 2019 11:29:01 -0800 Subject: rcutorture: Allow boottime stall warnings to be suppressed In normal production, an RCU CPU stall warning at boottime is often just as bad as at any other time. In fact, given the desire for fast boot, any sort of long-term stall at boot is a bad idea. However, heavy rcutorture testing on large hyperthreaded systems can generate boottime RCU CPU stalls as a matter of course. This commit therefore provides a kernel boot parameter that suppresses reporting of boottime RCU CPU stall warnings and similarly of rcutorture writer stalls. Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index dbc22d684627..ee007b5c874f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4195,6 +4195,12 @@ rcupdate.rcu_cpu_stall_suppress= [KNL] Suppress RCU CPU stall warning messages. + rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] + Suppress RCU CPU stall warning messages and + rcutorture writer stall warnings that occur + during early boot, that is, during the time + before the init task is spawned. + rcupdate.rcu_cpu_stall_timeout= [KNL] Set timeout for RCU CPU stall warning messages. -- cgit v1.2.3 From 8171d3e0dafd37a9c833904e5a936f4154a1e95b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 6 Dec 2019 15:02:59 -0800 Subject: torture: Allow disabling of boottime CPU-hotplug torture operations In theory, RCU-hotplug operations are supposed to work as soon as there is more than one CPU online. However, in practice, in normal production there is no way to make them happen until userspace is up and running. Besides which, on smaller systems, rcutorture doesn't start doing hotplug operations until 30 seconds after the start of boot, which on most systems also means the better part of 30 seconds after the end of boot. This commit therefore provides a new torture.disable_onoff_at_boot kernel boot parameter that suppresses CPU-hotplug torture operations until about the time that init is spawned. Of course, if you know of a need for boottime CPU-hotplug operations, then you should avoid passing this argument to any of the torture tests. You might also want to look at the splats linked to below. Link: https://lore.kernel.org/lkml/20191206185208.GA25636@paulmck-ThinkPad-P72/ Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-parameters.txt | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index ee007b5c874f..868f59a48580 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4873,6 +4873,10 @@ topology updates sent by the hypervisor to this LPAR. + torture.disable_onoff_at_boot= [KNL] + Prevent the CPU-hotplug component of torturing + until after init has spawned. + tp720= [HW,PS2] tpm_suspend_pcr=[HW,TPM] -- cgit v1.2.3