From a7c8655b073d89303911c89d0fd9fc4be7631fbe Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 30 Nov 2017 15:36:35 -0800 Subject: sched/isolation: Eliminate NO_HZ_FULL_ALL Commit 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter") broke CONFIG_NO_HZ_FULL_ALL=y kernels. This breakage is due to the code under CONFIG_NO_HZ_FULL_ALL failing to invoke the shiny new housekeeping functions. This means that rcutorture scenario TREE04 now emits RCU CPU stall warnings due to the RCU grace-period kthreads not being awakened at a time of their choosing, or perhaps even not at all: [ 27.731422] rcu_bh kthread starved for 21001 jiffies! g18446744073709551369 c18446744073709551368 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=3 [ 27.731423] rcu_bh I14936 9 2 0x80080000 [ 27.731435] Call Trace: [ 27.731440] __schedule+0x31a/0x6d0 [ 27.731442] schedule+0x31/0x80 [ 27.731446] schedule_timeout+0x15a/0x320 [ 27.731453] ? call_timer_fn+0x130/0x130 [ 27.731457] rcu_gp_kthread+0x66c/0xea0 [ 27.731458] ? rcu_gp_kthread+0x66c/0xea0 Because no one has complained about CONFIG_NO_HZ_FULL_ALL=y being broken, I hypothesize that no one is in fact using it, other than rcutorture. This commit therefore eliminates CONFIG_NO_HZ_FULL_ALL and updates rcutorture's config files to instead use the nohz_full= kernel parameter to put the desired CPUs into nohz_full mode. Fixes: 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter") Reported-by: kernel test robot Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Thomas Gleixner Cc: Chris Metcalf Cc: Christoph Lameter Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Rik van Riel Cc: Wanpeng Li Cc: Ingo Molnar Cc: John Stultz Cc: Jonathan Corbet --- Documentation/timers/NO_HZ.txt | 7 ------- 1 file changed, 7 deletions(-) (limited to 'Documentation/timers') diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt index 2dcaf9adb7a7..9591092da5e0 100644 --- a/Documentation/timers/NO_HZ.txt +++ b/Documentation/timers/NO_HZ.txt @@ -131,13 +131,6 @@ error message, and the boot CPU will be removed from the mask. Note that this means that your system must have at least two CPUs in order for CONFIG_NO_HZ_FULL=y to do anything for you. -Alternatively, the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter specifies -that all CPUs other than the boot CPU are adaptive-ticks CPUs. This -Kconfig parameter will be overridden by the "nohz_full=" boot parameter, -so that if both the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter and -the "nohz_full=1" boot parameter is specified, the boot parameter will -prevail so that only CPU 1 will be an adaptive-ticks CPU. - Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded. This is covered in the "RCU IMPLICATIONS" section below. -- cgit