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authorLinus Torvalds <torvalds@linux-foundation.org>2008-05-10 23:58:02 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-05-10 23:58:02 -0400
commit8e3e076c5a78519a9f64cd384e8f18bc21882ce0 (patch)
treef032258fde3aa4771e86bf4552fe4530c221dec3 /arch/mn10300/Kconfig
parent00b41ec2611dc98f87f30753ee00a53db648d662 (diff)
BKL: revert back to the old spinlock implementation
The generic semaphore rewrite had a huge performance regression on AIM7 (and potentially other BKL-heavy benchmarks) because the generic semaphores had been rewritten to be simple to understand and fair. The latter, in particular, turns a semaphore-based BKL implementation into a mess of scheduling. The attempt to fix the performance regression failed miserably (see the previous commit 00b41ec2611dc98f87f30753ee00a53db648d662 'Revert "semaphore: fix"'), and so for now the simple and sane approach is to instead just go back to the old spinlock-based BKL implementation that never had any issues like this. This patch also has the advantage of being reported to fix the regression completely according to Yanmin Zhang, unlike the semaphore hack which still left a couple percentage point regression. As a spinlock, the BKL obviously has the potential to be a latency issue, but it's not really any different from any other spinlock in that respect. We do want to get rid of the BKL asap, but that has been the plan for several years. These days, the biggest users are in the tty layer (open/release in particular) and Alan holds out some hope: "tty release is probably a few months away from getting cured - I'm afraid it will almost certainly be the very last user of the BKL in tty to get fixed as it depends on everything else being sanely locked." so while we're not there yet, we do have a plan of action. Tested-by: Yanmin Zhang <yanmin_zhang@linux.intel.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Andi Kleen <andi@firstfloor.org> Cc: Matthew Wilcox <matthew@wil.cx> Cc: Alexander Viro <viro@ftp.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/mn10300/Kconfig')
-rw-r--r--arch/mn10300/Kconfig11
1 files changed, 0 insertions, 11 deletions
diff --git a/arch/mn10300/Kconfig b/arch/mn10300/Kconfig
index 6a6409adc564..e856218da90d 100644
--- a/arch/mn10300/Kconfig
+++ b/arch/mn10300/Kconfig
@@ -186,17 +186,6 @@ config PREEMPT
186 Say Y here if you are building a kernel for a desktop, embedded 186 Say Y here if you are building a kernel for a desktop, embedded
187 or real-time system. Say N if you are unsure. 187 or real-time system. Say N if you are unsure.
188 188
189config PREEMPT_BKL
190 bool "Preempt The Big Kernel Lock"
191 depends on PREEMPT
192 default y
193 help
194 This option reduces the latency of the kernel by making the
195 big kernel lock preemptible.
196
197 Say Y here if you are building a kernel for a desktop system.
198 Say N if you are unsure.
199
200config MN10300_CURRENT_IN_E2 189config MN10300_CURRENT_IN_E2
201 bool "Hold current task address in E2 register" 190 bool "Hold current task address in E2 register"
202 default y 191 default y