From: Miao Yan yanmiaobest@gmail.com
When running SMP configuration on QEMU (tcg mode, no kvm), there is a busy loop in start_aps(), calling udelay(), that waits for APs to show up online. However, there is a chance that VCPU1 will be timeout waiting, IOW the secondary VCPUs haven't started their execution yet.
This patch adds a 'pause' instruction in __udelay() only for QEMU target, to give other VCPUs a chance to run. When QEMU sees the 'pause' instruction, it will yeild the execution to other CPUs.
Signed-off-by: Miao Yan yanmiaobest@gmail.com Signed-off-by: Bin Meng bmeng.cn@gmail.com ---
arch/x86/lib/tsc_timer.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/x86/lib/tsc_timer.c b/arch/x86/lib/tsc_timer.c index 7f5ba2c..0df1af2 100644 --- a/arch/x86/lib/tsc_timer.c +++ b/arch/x86/lib/tsc_timer.c @@ -355,7 +355,15 @@ void __udelay(unsigned long usec) stop = now + usec * get_tbclk_mhz();
while ((int64_t)(stop - get_ticks()) > 0) +#if defined(CONFIG_QEMU) && defined(CONFIG_SMP) + /* + * Add a 'pause' instruction on qemu target, + * to give other VCPUs a chance to run. + */ + asm volatile("pause"); +#else ; +#endif }
int timer_init(void)