Revert "cherry-pick scheduler fix to avoid temporary VM freezes on NUMA hosts"

This reverts commit 29cb6fcbb7, user
feedback was showing any positive impact of this patch, and upstream
still hasn't a fix for older stable releases (but for 6.8), so for now
rather revert this and wait for either a better (well, actual) fix or
updating to 6.8 or newer.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

patches/kernel/0015-sched-core-Drop-spinlocks-on-contention-iff-kernel-i.patch

@@ -1,75 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Sean Christopherson <seanjc@google.com>
-Date: Wed, 10 Jan 2024 13:47:23 -0800
-Subject: [PATCH] sched/core: Drop spinlocks on contention iff kernel is
- preemptible
-
-Use preempt_model_preemptible() to detect a preemptible kernel when
-deciding whether or not to reschedule in order to drop a contended
-spinlock or rwlock.  Because PREEMPT_DYNAMIC selects PREEMPTION, kernels
-built with PREEMPT_DYNAMIC=y will yield contended locks even if the live
-preemption model is "none" or "voluntary".  In short, make kernels with
-dynamically selected models behave the same as kernels with statically
-selected models.
-
-Somewhat counter-intuitively, NOT yielding a lock can provide better
-latency for the relevant tasks/processes.  E.g. KVM x86's mmu_lock, a
-rwlock, is often contended between an invalidation event (takes mmu_lock
-for write) and a vCPU servicing a guest page fault (takes mmu_lock for
-read).  For _some_ setups, letting the invalidation task complete even
-if there is mmu_lock contention provides lower latency for *all* tasks,
-i.e. the invalidation completes sooner *and* the vCPU services the guest
-page fault sooner.
-
-But even KVM's mmu_lock behavior isn't uniform, e.g. the "best" behavior
-can vary depending on the host VMM, the guest workload, the number of
-vCPUs, the number of pCPUs in the host, why there is lock contention, etc.
-
-In other words, simply deleting the CONFIG_PREEMPTION guard (or doing the
-opposite and removing contention yielding entirely) needs to come with a
-big pile of data proving that changing the status quo is a net positive.
-
-Cc: Valentin Schneider <valentin.schneider@arm.com>
-Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
-Cc: Marco Elver <elver@google.com>
-Cc: Frederic Weisbecker <frederic@kernel.org>
-Cc: David Matlack <dmatlack@google.com>
-Signed-off-by: Sean Christopherson <seanjc@google.com>
----
- include/linux/sched.h | 14 ++++++--------
- 1 file changed, 6 insertions(+), 8 deletions(-)
-
-diff --git a/include/linux/sched.h b/include/linux/sched.h
-index 609bde814cb0..995e6699e026 100644
---- a/include/linux/sched.h
-+++ b/include/linux/sched.h
-@@ -2211,11 +2211,10 @@ static inline bool preempt_model_preemptible(void)
-  */
- static inline int spin_needbreak(spinlock_t *lock)
- {
--#ifdef CONFIG_PREEMPTION
-+	if (!preempt_model_preemptible())
-+		return 0;
-+
- 	return spin_is_contended(lock);
--#else
--	return 0;
--#endif
- }
- 
- /*
-@@ -2228,11 +2227,10 @@ static inline int spin_needbreak(spinlock_t *lock)
-  */
- static inline int rwlock_needbreak(rwlock_t *lock)
- {
--#ifdef CONFIG_PREEMPTION
-+	if (!preempt_model_preemptible())
-+		return 0;
-+
- 	return rwlock_is_contended(lock);
--#else
--	return 0;
--#endif
- }
- 
- static __always_inline bool need_resched(void)