Commit-ID: 2d99af8e8fd6c2dea11ab539f7aba69c37b845b4 Gitweb: http://git.kernel.org/tip/2d99af8e8fd6c2dea11ab539f7aba69c37b845b4 Author: Len Brown <[email protected]> AuthorDate: Sun, 16 Aug 2015 11:45:46 -0400 Committer: Ingo Molnar <[email protected]> CommitDate: Mon, 17 Aug 2015 10:42:27 +0200
x86/smpboot: Remove udelay(100) when polling cpu_callin_map 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]> Cc: Andy Lutomirski <[email protected]> Cc: Arjan van de Ven <[email protected]> Cc: Boris Ostrovsky <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Igor Mammedov <[email protected]> Cc: Jan H. Schönherr <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Zhu Guihua <[email protected]> Link: http://lkml.kernel.org/r/0aade12eabeb89a688c929fe80856eaea0544bb7.1439739165.git.len.br...@intel.com Signed-off-by: Ingo Molnar <[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(); } } -- 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/
