Linux makes a habit of writing the same value to the SCTLR that it
already holds. In a sample boot of the kernel to a shell prompt
it wrote the SCTLR with the value it already held 325465 times,
and wrote different values just 3 times.
Skip flushing the TLB if the SCTLR value isn't actually being changed;
this speeds up my sample boot by 3-5%.
Reported-by: Laurent Desnogues <laurent.desnog...@gmail.com>
Reviewed-by: Laurent Desnogues <laurent.desnog...@gmail.com>
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
Message-id: 1399560029-19007-1-git-send-email-peter.mayd...@linaro.org
---
target-arm/helper.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/target-arm/helper.c b/target-arm/helper.c
index 3be917c..417161e 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -2081,6 +2081,13 @@ static void sctlr_write(CPUARMState *env, const
ARMCPRegInfo *ri,
{
ARMCPU *cpu = arm_env_get_cpu(env);
+ if (env->cp15.c1_sys == value) {
+ /* Skip the TLB flush if nothing actually changed; Linux likes
+ * to do a lot of pointless SCTLR writes.
+ */
+ return;
+ }
+
env->cp15.c1_sys = value;
/* ??? Lots of these bits are not implemented. */
/* This may enable/disable the MMU, so do a TLB flush. */
--
1.9.2
