s390: Remove GENERIC_LOCKBREAK Kconfig option

s390 selects GENERIC_LOCKBREAK if PREEMPT is enabled. Reason is a historic
18 years old commit [1] which fixed a compile error for PREEMPT enabled
kernels. Back than only PREEMPT_NONE and PREEMPT_VOLUNTARY kernels were
considered to be important for s390. PREEMPT should "just work".

However, since recently PREEMPT is always enabled [2], which also causes
GENERIC_LOCKBREAK to be always enabled. For some workloads this leads to
massive performance degradation; e.g. a simple kernel compile on machines
with many CPUs may take up to four times longer.

To fix this just remove the GENERIC_LOCKBREAK from s390's Kconfig, since
the compile error from 18 years ago does not exist anymore.

[1] commit b6b40c532a36 ("[S390] Define GENERIC_LOCKBREAK.")
[2] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")

Cc: stable@vger.kernel.org
Reported-by: Massimiliano Pellizzer <massimiliano.pellizzer@canonical.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index ecbcbb781e40aa8cf3b0ef160b447bcb51eafde2..9921a3772bf737b49f68504522fb6775667b93a4 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -29,9 +29,6 @@ config GENERIC_BUG
 config GENERIC_BUG_RELATIVE_POINTERS
        def_bool y
 
-config GENERIC_LOCKBREAK
-       def_bool y if PREEMPTION
-
 config AUDIT_ARCH
        def_bool y