Messages in this thread | | | Date | Tue, 31 Jan 2012 13:43:41 +0100 | From | Ingo Molnar <> | Subject | Re: x86: clean up smpboot.c's use of udelay+schedule |
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* Arjan van de Ven <arjan@infradead.org> wrote:
> >From 9f8dd2b15ff19ad73ee0eb235b4fdde9277185e8 Mon Sep 17 00:00:00 2001 > From: Arjan van de Ven <arjan@linux.intel.com> > Date: Mon, 30 Jan 2012 20:38:09 -0800 > Subject: [PATCH] x86: clean up smpboot.c's use of udelay+schedule > > smpboot.c does a udelay() followed by a schedule(); to yield > the CPU to other threads. This comes from the time when the kernel > did not yet have usleep_*() style APIs... > > ... nowadays, the kernel can do better than this, and this > patch replaces this code sequence with a usleep_range(), > so that the CPU is actually yielded for some real time. > > Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> > --- > arch/x86/kernel/smpboot.c | 3 +-- > 1 files changed, 1 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 66d250c..0b794c6 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -781,14 +781,13 @@ do_rest: > for (timeout = 0; timeout < 50000; timeout++) { > if (cpumask_test_cpu(cpu, cpu_callin_mask)) > break; /* It has booted */ > - udelay(100); > /* > * Allow other tasks to run while we wait for the > * AP to come online. This also gives a chance > * for the MTRR work(triggered by the AP coming online) > * to be completed in the stop machine context. > */ > - schedule(); > + usleep_range(100, 200);
I'm wondering whether we could shorten this delay to say 10 usecs and thus save 0.1 msecs (or more) from a typical SMP bootup?
Thanks,
Ingo
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