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SubjectRe: native_cpu_up speed (Re: [PATCH] x86: skip delays during SMP initialization similar to Xen)
On 05/29/2015 09:47 AM, Len Brown wrote:
> However, a clear pattern jumped out of the trace for how long
> the BSP waits for the AP to set itself in cpu_callin_mask.
> This is the time in start secondary where cpu_init() is running,
> up through smp_callin() is called.
> On the 1st package, each remote AP take 9 delays = 900 us to do this,
> whether they are new cores or HT siblings of cores already up.
> But the 1st processor on remote_packages_ aka nodes, takes 60,000 us
> No typo -- that is 60ms!

That does sound like calibrate_delay(), which "waits" for 5 * (10ms + 1 tick)
on each newly encountered package...


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