From 6e38f1e79d16f4fa9e5cf06792500e11c96a6f84 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Sun, 16 Aug 2015 11:45:45 -0400 Subject: [PATCH] x86/smpboot: Remove udelay(100) when polling cpu_initialized_map MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit After the BSP sends the APIC INIT/SIPI/SIPI to the AP, it waits for the AP to come up and indicate that it is alive by setting its own bit in the cpu_initialized_mask. Linux polls for up to 10 seconds for this to happen. Each polling loop has a udelay(100) and a call to schedule(). The udelay(100) adds no value. For example, on my desktop, the BSP waits for the other 3 CPUs to come on line at boot for 305, 404, 405 usec. For resume from S3, it waits 317, 404, 405 usec. But when the udelay(100) is removed, the BSP waits 305, 310, 306 for boot, and 305, 307, 306 for resume. So for both boot and resume, removing the udelay(100) speeds online by about 100us in 2 of 3 cases. Signed-off-by: Len Brown Cc: Andy Lutomirski Cc: Arjan van de Ven Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Dave Hansen Cc: Igor Mammedov Cc: Jan H. Schönherr Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Zhu Guihua Link: http://lkml.kernel.org/r/33ef746c67d2489cad0a9b1958cf71167232ff2b.1439739165.git.len.brown@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index b1f3ed9c7a9e..9ad88fb0a303 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -898,7 +898,7 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) if (!boot_error) { /* - * Wait 10s total for a response from AP + * Wait 10s total for first sign of life from AP */ boot_error = -1; timeout = jiffies + 10*HZ; @@ -911,7 +911,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) boot_error = 0; break; } - udelay(100); schedule(); } } -- 2.34.1