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 <[email protected]> Signed-off-by: Peter Maydell <[email protected]> --- I believe there are kernel patches in the works to avoid being quite so profligate with SCTLR writes, but there are still a lot of older kernels out in the world, so this is worth having IMHO. 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
