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| Started by | raghu MG <raghumag@gmail.com> |
|---|---|
| First post | 2015-10-26 07:50 +0100 |
| Last post | 2015-10-30 12:00 +0100 |
| Articles | 3 — 2 participants |
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How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? raghu MG <raghumag@gmail.com> - 2015-10-26 07:50 +0100
Re: How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-26 11:50 +0100
Re: How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? raghu MG <raghumag@gmail.com> - 2015-10-30 12:00 +0100
| From | raghu MG <raghumag@gmail.com> |
|---|---|
| Date | 2015-10-26 07:50 +0100 |
| Subject | How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? |
| Message-ID | <qnJLs-4TL-19@gated-at.bofh.it> |
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? -- 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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| From | Russell King - ARM Linux <linux@arm.linux.org.uk> |
|---|---|
| Date | 2015-10-26 11:50 +0100 |
| Subject | Re: How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? |
| Message-ID | <qnNvI-78a-37@gated-at.bofh.it> |
| In reply to | #1255699 |
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. -- 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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| From | raghu MG <raghumag@gmail.com> |
|---|---|
| Date | 2015-10-30 12:00 +0100 |
| Subject | Re: How is jiffies upation while holding spinlock in Uniprocessor or SMP environment? |
| Message-ID | <qpfzA-4Mx-7@gated-at.bofh.it> |
| In reply to | #1255814 |
Thank you for clarifying. On Mon, Oct 26, 2015 at 4:18 PM, Russell King - ARM Linux <linux@arm.linux.org.uk> 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. -- 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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