From: Len Brown Date: Fri, 16 Oct 2015 00:14:29 -0400 Subject: x86/smpboot: Fix CPU #1 boot timeout Origin: https://git.kernel.org/linus/fcafddec4e78a7776db4b6685db6b2902d4300fc Bug-Debian: https://bugs.debian.org/802464 The following commit: a9bcaa02a5104ac ("x86/smpboot: Remove SIPI delays from cpu_up()") Caused some Intel Core2 processors to time-out when bringing up CPU #1, resulting in the missing of that CPU after bootup. That patch reduced the SIPI delays from udelay() 300, 200 to udelay() 0, 0 on modern processors. Several Intel(R) Core(TM)2 systems failed to bring up CPU #1 10/10 times after that change. Increasing either of the SIPI delays to udelay(1) results in success. So here we increase both to udelay(10). While this may be 20x slower than the absolute minimum, it is still 20x to 30x faster than the original code. Tested-by: Donald Parsons Tested-by: Shane Signed-off-by: Len Brown Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dparsons@brightdsl.net Cc: shrybman@teksavvy.com Link: http://lkml.kernel.org/r/6dd554ee8945984d85aafb2ad35793174d068af0.1444968087.git.len.brown@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -657,7 +657,9 @@ wakeup_secondary_cpu_via_init(int phys_a /* * Give the other CPU some time to accept the IPI. */ - if (init_udelay) + if (init_udelay == 0) + udelay(10); + else udelay(300); pr_debug("Startup point 1\n"); @@ -668,7 +670,9 @@ wakeup_secondary_cpu_via_init(int phys_a /* * Give the other CPU some time to accept the IPI. */ - if (init_udelay) + if (init_udelay == 0) + udelay(10); + else udelay(200); if (maxlvt > 3) /* Due to the Pentium erratum 3AP. */