| Message ID | 20220722002825.GA2848736@paulmck-ThinkPad-P17-Gen-1 (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 4ba1329cbb9456c937bff1ed8ad4ca91ab75eab6 |
| Headers | show |
| Series | [GIT,PULL] Urgent fix for expedited SRCU v5.19 boot-speed regression | expand |
The pull request you sent on Thu, 21 Jul 2022 17:28:25 -0700:
> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git tags/rcu-urgent.2022.07.21a
has been merged into torvalds/linux.git:
https://git.kernel.org/torvalds/c/4ba1329cbb9456c937bff1ed8ad4ca91ab75eab6
Thank you!
Hello, Linus, This pull request fixes a severe boot-speed regression for embedded systems running in virtual environments, which are commonly used for development and debugging. This regression bloats the edit/compile/boot/debug cycle, causing considerable pain. Hence the urgent pull request into v5.19 rather than waiting for the upcoming merge window. The following changes since commit a111daf0c53ae91e71fd2bfe7497862d14132e3e: Linux 5.19-rc3 (2022-06-19 15:06:47 -0500) are available in the Git repository at: git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git tags/rcu-urgent.2022.07.21a for you to fetch changes up to 4f2bfd9494a072d58203600de6bedd72680e612a: srcu: Make expedited RCU grace periods block even less frequently (2022-07-19 11:39:59 -0700) ---------------------------------------------------------------- Urgent RCU pull request for v5.19 This pull request 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, hence this pull request. ---------------------------------------------------------------- Neeraj Upadhyay (1): srcu: Make expedited RCU grace periods block even less frequently Paul E. McKenney (1): srcu: Block less aggressively for expedited grace periods Documentation/admin-guide/kernel-parameters.txt | 18 +++++ kernel/rcu/srcutree.c | 98 +++++++++++++++++++------ 2 files changed, 92 insertions(+), 24 deletions(-)