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

[raghu MG]

Thank you for clarifying.

On Mon, Oct 26, 2015 at 4:18 PM, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxxx> wrote:
> On Mon, Oct 26, 2015 at 12:19:31PM +0530, raghu MG wrote:
>> 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?
>
> It isn't, and...
>>
>> 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?
>
> You can't rely on jiffies being updated while holding a spinlock.
> Expecting jiffies to update while holding a spinlock is a bug.
>
> --
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
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