From: Len Brown <[email protected]> After the BSP sends INIT/SIPI/SIP to the AP and sees the AP in the cpu_initialized_map, it sets the AP loose via the cpu_callout_map, and waits for it via the cpu_callin_map.
The BSP polls the cpu_callin_map with a udelay(100) and a schedule() in each iteration. The udelay(100) adds no value. For example, on my 4-CPU dekstop, the AP finishes cpu_callin() in under 70 usec and sets the cpu_callin_mask. The BSP, however, doesn't see that setting until over 30 usec later, because it was still running its udelay(100) when the AP finished. Deleting the udelay(100) in the cpu_callin_mask polling loop, saves from 0 to 100 usec per Application Processor. Signed-off-by: Len Brown <[email protected]> --- arch/x86/kernel/smpboot.c | 1 - 1 file changed, 1 deletion(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 9ad88fb..310b6f0 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -926,7 +926,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) * for the MTRR work(triggered by the AP coming online) * to be completed in the stop machine context. */ - udelay(100); schedule(); } } -- 2.5.0.330.g130be8e -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
