On 8/22/21 10:01 AM, Rui Salvaterra wrote:
Based on the existing documentation [1][2], I dare anyone to demonstrate that we need to fine-tune these RCU parameters. The (performance) breakage potential for doing so is immense, so let's just please put down this loaded footgun. Disable CONFIG_RCU_EXPERT and dependent symbols.[1] https://www.kernel.org/doc/Documentation/RCU/Design/Data-Structures/Data-Structures.html [2] https://lwn.net/Articles/777214/ Signed-off-by: Rui Salvaterra <rsalvate...@gmail.com>
There are also some targets which explicitly unset CONFIG_RCU_EXPERT: $ git grep CONFIG_RCU_EXPERT target/linux/gemini/config-5.10:# CONFIG_RCU_EXPERT is not set target/linux/gemini/config-5.4:# CONFIG_RCU_EXPERT is not set target/linux/generic/config-5.10:CONFIG_RCU_EXPERT=y target/linux/generic/config-5.4:CONFIG_RCU_EXPERT=y target/linux/ipq807x/config-default:# CONFIG_RCU_EXPERT is not set target/linux/layerscape/armv7/config-5.4:# CONFIG_RCU_EXPERT is not set target/linux/layerscape/armv8_64b/config-5.4:# CONFIG_RCU_EXPERT is not set target/linux/mediatek/mt7623/config-5.10:# CONFIG_RCU_EXPERT is not set target/linux/oxnas/ox810se/config-default:# CONFIG_RCU_EXPERT is not set target/linux/oxnas/ox820/config-default:# CONFIG_RCU_EXPERT is not set target/linux/rockchip/armv8/config-5.10:# CONFIG_RCU_EXPERT is not set target/linux/rockchip/armv8/config-5.4:# CONFIG_RCU_EXPERT is not set target/linux/tegra/config-5.10:# CONFIG_RCU_EXPERT is not set target/linux/tegra/config-5.4:# CONFIG_RCU_EXPERT is not set This should be removed from the target config file.CONFIG_RCU_STALL_COMMON=y and CONFIG_RCU_NEED_SEGCBLIST=y are also set in most target configurations. Should we move them to the generic configuration?
Hauke
--- target/linux/generic/config-5.10 | 7 +------ target/linux/generic/config-5.4 | 6 +----- 2 files changed, 2 insertions(+), 11 deletions(-) diff --git a/target/linux/generic/config-5.10 b/target/linux/generic/config-5.10 index f944f1718f..91f137fbc3 100644 --- a/target/linux/generic/config-5.10 +++ b/target/linux/generic/config-5.10 @@ -4631,12 +4631,8 @@ CONFIG_PWRSEQ_SIMPLE=y CONFIG_RCU_CPU_STALL_TIMEOUT=60 # CONFIG_RCU_EQS_DEBUG is not set # CONFIG_RCU_EXPEDITE_BOOT is not set -CONFIG_RCU_EXPERT=y -CONFIG_RCU_FANOUT=32 -CONFIG_RCU_FANOUT_LEAF=16 -# CONFIG_RCU_FAST_NO_HZ is not set +# CONFIG_RCU_EXPERT is not set CONFIG_RCU_KTHREAD_PRIO=0 -# CONFIG_RCU_NOCB_CPU is not set # CONFIG_RCU_PERF_TEST is not set # CONFIG_RCU_REF_SCALE_TEST is not set # CONFIG_RCU_SCALE_TEST is not set @@ -5995,7 +5991,6 @@ CONFIG_SYSVIPC_SYSCTL=y # CONFIG_TARGET_CORE is not set # CONFIG_TASKSTATS is not set # CONFIG_TASKS_RCU is not set -CONFIG_TASKS_TRACE_RCU_READ_MB=y # CONFIG_TASK_XACCT is not set # CONFIG_TC35815 is not set # CONFIG_TCG_ATMEL is not set diff --git a/target/linux/generic/config-5.4 b/target/linux/generic/config-5.4 index 45d8f0976e..06f5e43a6d 100644 --- a/target/linux/generic/config-5.4 +++ b/target/linux/generic/config-5.4 @@ -4262,12 +4262,8 @@ CONFIG_PWRSEQ_SIMPLE=y CONFIG_RCU_CPU_STALL_TIMEOUT=60 # CONFIG_RCU_EQS_DEBUG is not set # CONFIG_RCU_EXPEDITE_BOOT is not set -CONFIG_RCU_EXPERT=y -CONFIG_RCU_FANOUT=32 -CONFIG_RCU_FANOUT_LEAF=16 -# CONFIG_RCU_FAST_NO_HZ is not set +# CONFIG_RCU_EXPERT is not set CONFIG_RCU_KTHREAD_PRIO=0 -# CONFIG_RCU_NOCB_CPU is not set # CONFIG_RCU_PERF_TEST is not set # CONFIG_RCU_TORTURE_TEST is not set CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY=3
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