diff mbox

[PULL,10/17] target-arm/helper.c: Don't flush the TLB if SCTLR is rewritten unchanged

Message ID 1399995099-26635-11-git-send-email-peter.maydell@linaro.org
State Accepted
Commit 2f0d8631b74c873c8867a7b509335bc2bf8d8886
Headers show

Commit Message

Peter Maydell May 13, 2014, 3:31 p.m. UTC 
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.desnogues@gmail.com>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1399560029-19007-1-git-send-email-peter.maydell@linaro.org
---
 target-arm/helper.c | 7 +++++++
 1 file changed, 7 insertions(+)
diff mbox

Patch

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.  */