How is jiffies upation while holding spinlock in Uniprocessor or SMP environment?

[raghu MG]

Hello,
I have couple of questions.
1) In case of UP how is jiffies(timer) get updated while holding spin
lock using spinlock_irq_save?

2)My understanding is in smp environment jiffies updation cannot be
done on processor holding spinlock irrespective of spinlock API.So
timer interrupt should be enabled across all cores in SoC. Imagine a
scenario in quad core processor where 4 cores are holding 4 different
spinlocks & how is the timer interrupt for jiffies handled?
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