From bf29cb238dc0656e6564b6a94bb82e11d2129437 Mon Sep 17 00:00:00 2001 From: Paul E. McKenney Date: Thu, 14 Dec 2017 19:18:25 +0100 Subject: sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION CONFIG_NO_HZ_FULL doesn't make sense without CONFIG_CPU_ISOLATION. In fact enabling the first without the second is a regression as nohz_full= boot parameter gets silently ignored. Besides this unnatural combination hangs RCU gp kthread when running rcutorture for reasons that are not yet fully understood: rcu_preempt kthread starved for 9974 jiffies! g4294967208 +c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0 rcu_preempt I 7464 8 2 0x80000000 Call Trace: __schedule+0x493/0x620 schedule+0x24/0x40 schedule_timeout+0x330/0x3b0 ? preempt_count_sub+0xea/0x140 ? collect_expired_timers+0xb0/0xb0 rcu_gp_kthread+0x6bf/0xef0 This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which prevents all these bad behaviours. Reported-by: kernel test robot Signed-off-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Chris Metcalf Cc: Christoph Lameter Cc: John Stultz Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Wanpeng Li Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL") Link: http://lkml.kernel.org/r/1513275507-29200-2-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar --- kernel/time/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index e776fc8cc1df..f6b5f19223d6 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -95,6 +95,7 @@ config NO_HZ_FULL select RCU_NOCB_CPU select VIRT_CPU_ACCOUNTING_GEN select IRQ_WORK + select CPU_ISOLATION help Adaptively try to shutdown the tick whenever possible, even when the CPU is running tasks. Typically this requires running a single -- cgit v1.2.3 From 2c43838c99d9d23f17eb2bdadafcb2879cca6995 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 14 Dec 2017 19:18:26 +0100 Subject: sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default The "isolcpus=" boot parameter support was always built-in before we moved the related code under CONFIG_CPU_ISOLATION. Having it disabled by default is very confusing for people accustomed to use this parameter. So enable it by dafault to keep the previous behaviour but keep it optable for those who want to tinify their kernels. Signed-off-by: Frederic Weisbecker Cc: Chris Metcalf Cc: Christoph Lameter Cc: John Stultz Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Wanpeng Li Cc: kernel test robot Link: http://lkml.kernel.org/r/1513275507-29200-3-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar --- init/Kconfig | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/init/Kconfig b/init/Kconfig index 2934249fba46..690a381adee0 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -461,10 +461,14 @@ endmenu # "CPU/Task time and stats accounting" config CPU_ISOLATION bool "CPU isolation" + default y help Make sure that CPUs running critical tasks are not disturbed by any source of "noise" such as unbound workqueues, timers, kthreads... - Unbound jobs get offloaded to housekeeping CPUs. + Unbound jobs get offloaded to housekeeping CPUs. This is driven by + the "isolcpus=" boot parameter. + + Say Y if unsure. source "kernel/rcu/Kconfig" -- cgit v1.2.3 From d94d105329e4a8a874853b5bd854b6587c41adda Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 14 Dec 2017 19:18:27 +0100 Subject: sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION=y The "isolcpus=" and "nohz_full=" boot parameters depend on CPU Isolation support. Let's document that. Signed-off-by: Frederic Weisbecker Cc: Chris Metcalf Cc: Christoph Lameter Cc: John Stultz Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Wanpeng Li Cc: kernel test robot Link: http://lkml.kernel.org/r/1513275507-29200-4-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar --- Documentation/admin-guide/kernel-parameters.rst | 1 + Documentation/admin-guide/kernel-parameters.txt | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst index b2598cc9834c..7242cbda15dd 100644 --- a/Documentation/admin-guide/kernel-parameters.rst +++ b/Documentation/admin-guide/kernel-parameters.rst @@ -109,6 +109,7 @@ parameter is applicable:: IPV6 IPv6 support is enabled. ISAPNP ISA PnP code is enabled. ISDN Appropriate ISDN support is enabled. + ISOL CPU Isolation is enabled. JOY Appropriate joystick support is enabled. KGDB Kernel debugger support is enabled. KVM Kernel Virtual Machine support is enabled. diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 6571fbfdb2a1..168310707ec2 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1737,7 +1737,7 @@ isapnp= [ISAPNP] Format: ,,, - isolcpus= [KNL,SMP] Isolate a given set of CPUs from disturbance. + isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. [Deprecated - use cpusets instead] Format: [flag-list,] @@ -2662,7 +2662,7 @@ Valid arguments: on, off Default: on - nohz_full= [KNL,BOOT] + nohz_full= [KNL,BOOT,SMP,ISOL] The argument is a cpu list, as described above. In kernels built with CONFIG_NO_HZ_FULL=y, set the specified list of CPUs whose tick will be stopped -- cgit v1.2.3