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authorLinus Torvalds <torvalds@linux-foundation.org>2022-07-22 10:01:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-07-22 10:01:20 -0700
commit4ba1329cbb9456c937bff1ed8ad4ca91ab75eab6 (patch)
tree0896381b07a5a82d5b7821284f38df9acb98b6d4 /Documentation/admin-guide
parent7fb5e508319068de1d69e6d7230416c390cb3cbb (diff)
parent4f2bfd9494a072d58203600de6bedd72680e612a (diff)
Merge tag 'rcu-urgent.2022.07.21a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU fix from Paul McKenney: "This contains a pair of commits that fix 282d8998e997 ("srcu: Prevent expedited GPs and blocking readers from consuming CPU"), which was itself a fix to an SRCU expedited grace-period problem that could prevent kernel live patching (KLP) from completing. That SRCU fix for KLP introduced large (as in minutes) boot-time delays to embedded Linux kernels running on qemu/KVM. These delays were due to the emulation of certain MMIO operations controlling memory layout, which were emulated with one expedited grace period per access. Common configurations required thousands of boot-time MMIO accesses, and thus thousands of boot-time expedited SRCU grace periods. In these configurations, the occasional sleeps that allowed KLP to proceed caused excessive boot delays. These commits preserve enough sleeps to permit KLP to proceed, but few enough that the virtual embedded kernels still boot reasonably quickly. This represents a regression introduced in the v5.19 merge window, and the bug is causing significant inconvenience" * tag 'rcu-urgent.2022.07.21a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: srcu: Make expedited RCU grace periods block even less frequently srcu: Block less aggressively for expedited grace periods
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt18
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2d26cb7e853..c0fdb04a0435 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5796,6 +5796,24 @@
expediting. Set to zero to disable automatic
expediting.
+ srcutree.srcu_max_nodelay [KNL]
+ Specifies the number of no-delay instances
+ per jiffy for which the SRCU grace period
+ worker thread will be rescheduled with zero
+ delay. Beyond this limit, worker thread will
+ be rescheduled with a sleep delay of one jiffy.
+
+ srcutree.srcu_max_nodelay_phase [KNL]
+ Specifies the per-grace-period phase, number of
+ non-sleeping polls of readers. Beyond this limit,
+ grace period worker thread will be rescheduled
+ with a sleep delay of one jiffy, between each
+ rescan of the readers, for a grace period phase.
+
+ srcutree.srcu_retry_check_delay [KNL]
+ Specifies number of microseconds of non-sleeping
+ delay between each non-sleeping poll of readers.
+
srcutree.small_contention_lim [KNL]
Specifies the number of update-side contention
events per jiffy will be tolerated before