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target-arm/helper.c: Don't flush the TLB if SCTLR is rewritten unchanged

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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
This commit is contained in:
Peter Maydell 2014-05-13 16:09:38 +01:00
parent 2e11986727
commit 2f0d8631b7
1 changed files with 7 additions and 0 deletions
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7
target-arm/helper.c
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@ -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. */