Commit fcafddec authored Oct 16, 2015 by Len Brown Committed by Ingo Molnar Oct 19, 2015

x86/smpboot: Fix CPU #1 boot timeout



The following commit:

  a9bcaa02 ("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 <dparsons@brightdsl.net>
Tested-by: Shane <shrybman@teksavvy.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>

parent f1ccd249

arch/x86/kernel/smpboot.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -660,7 +660,9 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
		/*
		* 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");
		@@ -671,7 +673,9 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
		/*
		* 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. */