Messages in this thread Patch in this message |  | | Date | Mon, 17 Aug 2015 09:28:24 -0700 | From | tip-bot for Len Brown <> | Subject | [tip:x86/boot] x86/smpboot: Remove udelay(100) when polling cpu_callin_map |
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Commit-ID: 2d99af8e8fd6c2dea11ab539f7aba69c37b845b4 Gitweb: http://git.kernel.org/tip/2d99af8e8fd6c2dea11ab539f7aba69c37b845b4 Author: Len Brown <len.brown@intel.com> AuthorDate: Sun, 16 Aug 2015 11:45:46 -0400 Committer: Ingo Molnar <mingo@kernel.org> 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 <len.brown@intel.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Jan H. Schönherr <jschoenh@amazon.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Zhu Guihua <zhugh.fnst@cn.fujitsu.com> Link: http://lkml.kernel.org/r/0aade12eabeb89a688c929fe80856eaea0544bb7.1439739165.git.len.brown@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- 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(); } }
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