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Groups > linux.kernel > #1208250
| From | Len Brown <lenb@kernel.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 2/4] x86 smpboot: remove udelay(100) when polling cpu_callin_map |
| Date | 2015-08-16 17:50 +0200 |
| Message-ID | <pY8m5-4qj-17@gated-at.bofh.it> (permalink) |
| References | <pY8m5-4qj-9@gated-at.bofh.it> |
| Organization | Intel Open Source Technology Center |
From: Len Brown <len.brown@intel.com> 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> --- 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(); } } -- 2.5.0.330.g130be8e -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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[PATCH 2/4] x86 smpboot: remove udelay(100) when polling cpu_callin_map Len Brown <lenb@kernel.org> - 2015-08-16 17:50 +0200 [tip:x86/boot] x86/smpboot: Remove udelay(100) when polling cpu_callin_map tip-bot for Len Brown <tipbot@zytor.com> - 2015-08-17 18:30 +0200
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