[v4,1/9] clocksource: arm_arch_timer: Gather KVM specific information in a structure
diff mbox

Message ID 1458842023-31853-2-git-send-email-julien.grall@arm.com
State New
Headers show

Commit Message

Julien Grall March 24, 2016, 5:53 p.m. UTC
Introduce a structure which are filled up by the arch timer driver and
used by the virtual timer in KVM.

The first member of this structure will be the timecounter. More members
will be added later.

A stub for the new helper isn't introduced because KVM requires the arch
timer for both ARM64 and ARM32.

The function arch_timer_get_timecounter is kept for the time being and
will be dropped in a subsequent patch.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>

    Changes in v3:
        - Rename the patch
        - Move the KVM changes and removal of arch_timer_get_timecounter
        in separate patches.
---
 drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
 include/clocksource/arm_arch_timer.h |  5 +++++
 2 files changed, 14 insertions(+), 3 deletions(-)

Comments

Daniel Lezcano March 29, 2016, 5:13 p.m. UTC | #1
On 03/24/2016 06:53 PM, Julien Grall wrote:
> Introduce a structure which are filled up by the arch timer driver and
> used by the virtual timer in KVM.
>
> The first member of this structure will be the timecounter. More members
> will be added later.
>
> A stub for the new helper isn't introduced because KVM requires the arch
> timer for both ARM64 and ARM32.
>
> The function arch_timer_get_timecounter is kept for the time being and
> will be dropped in a subsequent patch.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>

> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
>
>      Changes in v3:
>          - Rename the patch
>          - Move the KVM changes and removal of arch_timer_get_timecounter
>          in separate patches.
> ---
>   drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
>   include/clocksource/arm_arch_timer.h |  5 +++++
>   2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 5152b38..62bdfe7 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
>   	.mask	= CLOCKSOURCE_MASK(56),
>   };
>
> -static struct timecounter timecounter;
> +static struct arch_timer_kvm_info arch_timer_kvm_info;

This structure is statically defined in this subsystem but not used in 
this file and a couple of a accessors is added to let another subsystem 
to access it.

That sounds there is something wrong here with the design of the current 
code, virt/phys are mixed.

It isn't possible to split the virt/phys timer code respectively in 
virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?

At least, 'struct arch_timer_kvm_info' should belong to 
virt/kvm/arm/arch_timer.c.

> +struct arch_timer_kvm_info *arch_timer_get_kvm_info(void)
> +{
> +	return &arch_timer_kvm_info;
> +}
>
>   struct timecounter *arch_timer_get_timecounter(void)
>   {
> -	return &timecounter;
> +	return &arch_timer_kvm_info.timecounter;
>   }
>
>   static void __init arch_counter_register(unsigned type)
> @@ -500,7 +505,8 @@ static void __init arch_counter_register(unsigned type)
>   	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>   	cyclecounter.mult = clocksource_counter.mult;
>   	cyclecounter.shift = clocksource_counter.shift;
> -	timecounter_init(&timecounter, &cyclecounter, start_count);
> +	timecounter_init(&arch_timer_kvm_info.timecounter,
> +			 &cyclecounter, start_count);
>
>   	/* 56 bits minimum, so we assume worst case rollover */
>   	sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
> diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> index 25d0914..9101ed6b 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -49,11 +49,16 @@ enum arch_timer_reg {
>
>   #define ARCH_TIMER_EVT_STREAM_FREQ	10000	/* 100us */
>
> +struct arch_timer_kvm_info {
> +	struct timecounter timecounter;
> +};
> +
>   #ifdef CONFIG_ARM_ARCH_TIMER
>
>   extern u32 arch_timer_get_rate(void);
>   extern u64 (*arch_timer_read_counter)(void);
>   extern struct timecounter *arch_timer_get_timecounter(void);
> +extern struct arch_timer_kvm_info *arch_timer_get_kvm_info(void);
>
>   #else
>
>
Marc Zyngier March 29, 2016, 5:32 p.m. UTC | #2
Daniel,

On 29/03/16 18:13, Daniel Lezcano wrote:
> On 03/24/2016 06:53 PM, Julien Grall wrote:
>> Introduce a structure which are filled up by the arch timer driver and
>> used by the virtual timer in KVM.
>>
>> The first member of this structure will be the timecounter. More members
>> will be added later.
>>
>> A stub for the new helper isn't introduced because KVM requires the arch
>> timer for both ARM64 and ARM32.
>>
>> The function arch_timer_get_timecounter is kept for the time being and
>> will be dropped in a subsequent patch.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
> 
>> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>>
>>      Changes in v3:
>>          - Rename the patch
>>          - Move the KVM changes and removal of arch_timer_get_timecounter
>>          in separate patches.
>> ---
>>   drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
>>   include/clocksource/arm_arch_timer.h |  5 +++++
>>   2 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index 5152b38..62bdfe7 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
>>   	.mask	= CLOCKSOURCE_MASK(56),
>>   };
>>
>> -static struct timecounter timecounter;
>> +static struct arch_timer_kvm_info arch_timer_kvm_info;
> 
> This structure is statically defined in this subsystem but not used in 
> this file and a couple of a accessors is added to let another subsystem 
> to access it.
> 
> That sounds there is something wrong here with the design of the current 
> code, virt/phys are mixed.
> 
> It isn't possible to split the virt/phys timer code respectively in 
> virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?

No, that'd be the wrong thing to do. The kernel uses *either* the virt
or phys timer depending on how it has been booted, and both counters are
in use.

What KVM (or any other hypervisor) needs from the timer subsystem is:
- an interrupt (so that it can force a guest exit when the timer fires),
- a way to convert the values programmed into the HW into a timer event
(which is what the time counter structure is for).

That allows the hypervisor to *emulate* a timer for the guest, and
that's what virt/kvm/arm/arch_timer.c is all about. We have a clear
separation of what is driving the HW vs what is emulating it, and I'm
quite eager to preserve that.

> At least, 'struct arch_timer_kvm_info' should belong to 
> virt/kvm/arm/arch_timer.c.

At the cost of mandating separate storage in the arm_arch_timer driver.
I do not find that much nicer, but if you prefer that, fine by me.

Thanks,

	M.
Christoffer Dall March 30, 2016, 9:06 a.m. UTC | #3
On Tue, Mar 29, 2016 at 06:32:15PM +0100, Marc Zyngier wrote:
> Daniel,
> 
> On 29/03/16 18:13, Daniel Lezcano wrote:
> > On 03/24/2016 06:53 PM, Julien Grall wrote:
> >> Introduce a structure which are filled up by the arch timer driver and
> >> used by the virtual timer in KVM.
> >>
> >> The first member of this structure will be the timecounter. More members
> >> will be added later.
> >>
> >> A stub for the new helper isn't introduced because KVM requires the arch
> >> timer for both ARM64 and ARM32.
> >>
> >> The function arch_timer_get_timecounter is kept for the time being and
> >> will be dropped in a subsequent patch.
> >>
> >> Signed-off-by: Julien Grall <julien.grall@arm.com>
> > 
> >> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> >> Cc: Thomas Gleixner <tglx@linutronix.de>
> >> Cc: Marc Zyngier <marc.zyngier@arm.com>
> >>
> >>      Changes in v3:
> >>          - Rename the patch
> >>          - Move the KVM changes and removal of arch_timer_get_timecounter
> >>          in separate patches.
> >> ---
> >>   drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
> >>   include/clocksource/arm_arch_timer.h |  5 +++++
> >>   2 files changed, 14 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> >> index 5152b38..62bdfe7 100644
> >> --- a/drivers/clocksource/arm_arch_timer.c
> >> +++ b/drivers/clocksource/arm_arch_timer.c
> >> @@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
> >>   	.mask	= CLOCKSOURCE_MASK(56),
> >>   };
> >>
> >> -static struct timecounter timecounter;
> >> +static struct arch_timer_kvm_info arch_timer_kvm_info;
> > 
> > This structure is statically defined in this subsystem but not used in 
> > this file and a couple of a accessors is added to let another subsystem 
> > to access it.
> > 
> > That sounds there is something wrong here with the design of the current 
> > code, virt/phys are mixed.
> > 
> > It isn't possible to split the virt/phys timer code respectively in 
> > virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?
> 
> No, that'd be the wrong thing to do. The kernel uses *either* the virt
> or phys timer depending on how it has been booted, and both counters are
> in use.
> 
> What KVM (or any other hypervisor) needs from the timer subsystem is:
> - an interrupt (so that it can force a guest exit when the timer fires),
> - a way to convert the values programmed into the HW into a timer event
> (which is what the time counter structure is for).
> 
> That allows the hypervisor to *emulate* a timer for the guest, and
> that's what virt/kvm/arm/arch_timer.c is all about. We have a clear
> separation of what is driving the HW vs what is emulating it, and I'm
> quite eager to preserve that.
> 
> > At least, 'struct arch_timer_kvm_info' should belong to 
> > virt/kvm/arm/arch_timer.c.
> 
> At the cost of mandating separate storage in the arm_arch_timer driver.
> I do not find that much nicer, but if you prefer that, fine by me.
> 
If arch_timer_kvm_info is declared in virt/kvm/arm/arch_timer.c, then
do you want to make it globally accessible and populated by this code or
make it static to the KVM code and populate it with accessor functions?

To me the natural thing is that the arch timer driver maintains data
about the device it drives, and consumers of that data can ask the arch
timer driver for the details.

Thanks,
-Christoffer
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Marc Zyngier March 30, 2016, 9:12 a.m. UTC | #4
On 30/03/16 10:06, Christoffer Dall wrote:
> On Tue, Mar 29, 2016 at 06:32:15PM +0100, Marc Zyngier wrote:
>> Daniel,
>>
>> On 29/03/16 18:13, Daniel Lezcano wrote:
>>> On 03/24/2016 06:53 PM, Julien Grall wrote:
>>>> Introduce a structure which are filled up by the arch timer driver and
>>>> used by the virtual timer in KVM.
>>>>
>>>> The first member of this structure will be the timecounter. More members
>>>> will be added later.
>>>>
>>>> A stub for the new helper isn't introduced because KVM requires the arch
>>>> timer for both ARM64 and ARM32.
>>>>
>>>> The function arch_timer_get_timecounter is kept for the time being and
>>>> will be dropped in a subsequent patch.
>>>>
>>>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>>
>>>> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
>>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>>>>
>>>>      Changes in v3:
>>>>          - Rename the patch
>>>>          - Move the KVM changes and removal of arch_timer_get_timecounter
>>>>          in separate patches.
>>>> ---
>>>>   drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
>>>>   include/clocksource/arm_arch_timer.h |  5 +++++
>>>>   2 files changed, 14 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>>>> index 5152b38..62bdfe7 100644
>>>> --- a/drivers/clocksource/arm_arch_timer.c
>>>> +++ b/drivers/clocksource/arm_arch_timer.c
>>>> @@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
>>>>   	.mask	= CLOCKSOURCE_MASK(56),
>>>>   };
>>>>
>>>> -static struct timecounter timecounter;
>>>> +static struct arch_timer_kvm_info arch_timer_kvm_info;
>>>
>>> This structure is statically defined in this subsystem but not used in 
>>> this file and a couple of a accessors is added to let another subsystem 
>>> to access it.
>>>
>>> That sounds there is something wrong here with the design of the current 
>>> code, virt/phys are mixed.
>>>
>>> It isn't possible to split the virt/phys timer code respectively in 
>>> virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?
>>
>> No, that'd be the wrong thing to do. The kernel uses *either* the virt
>> or phys timer depending on how it has been booted, and both counters are
>> in use.
>>
>> What KVM (or any other hypervisor) needs from the timer subsystem is:
>> - an interrupt (so that it can force a guest exit when the timer fires),
>> - a way to convert the values programmed into the HW into a timer event
>> (which is what the time counter structure is for).
>>
>> That allows the hypervisor to *emulate* a timer for the guest, and
>> that's what virt/kvm/arm/arch_timer.c is all about. We have a clear
>> separation of what is driving the HW vs what is emulating it, and I'm
>> quite eager to preserve that.
>>
>>> At least, 'struct arch_timer_kvm_info' should belong to 
>>> virt/kvm/arm/arch_timer.c.
>>
>> At the cost of mandating separate storage in the arm_arch_timer driver.
>> I do not find that much nicer, but if you prefer that, fine by me.
>>
> If arch_timer_kvm_info is declared in virt/kvm/arm/arch_timer.c, then
> do you want to make it globally accessible and populated by this code or
> make it static to the KVM code and populate it with accessor functions?

That'd be the latter, as I'm really not fond of global data.

> To me the natural thing is that the arch timer driver maintains data
> about the device it drives, and consumers of that data can ask the arch
> timer driver for the details.

That was my approach too, and that's the way the code proposed by Julien
works. Daniel seems to have a different take on it though.

Thanks,

	M.
Daniel Lezcano March 30, 2016, 9:52 a.m. UTC | #5
On 03/30/2016 11:12 AM, Marc Zyngier wrote:
> On 30/03/16 10:06, Christoffer Dall wrote:
>> On Tue, Mar 29, 2016 at 06:32:15PM +0100, Marc Zyngier wrote:
>>> Daniel,
>>>
>>> On 29/03/16 18:13, Daniel Lezcano wrote:
>>>> On 03/24/2016 06:53 PM, Julien Grall wrote:
>>>>> Introduce a structure which are filled up by the arch timer driver and
>>>>> used by the virtual timer in KVM.
>>>>>
>>>>> The first member of this structure will be the timecounter. More members
>>>>> will be added later.
>>>>>
>>>>> A stub for the new helper isn't introduced because KVM requires the arch
>>>>> timer for both ARM64 and ARM32.
>>>>>
>>>>> The function arch_timer_get_timecounter is kept for the time being and
>>>>> will be dropped in a subsequent patch.
>>>>>
>>>>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>>>
>>>>> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
>>>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>>>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>>>>>
>>>>>       Changes in v3:
>>>>>           - Rename the patch
>>>>>           - Move the KVM changes and removal of arch_timer_get_timecounter
>>>>>           in separate patches.
>>>>> ---
>>>>>    drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
>>>>>    include/clocksource/arm_arch_timer.h |  5 +++++
>>>>>    2 files changed, 14 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>>>>> index 5152b38..62bdfe7 100644
>>>>> --- a/drivers/clocksource/arm_arch_timer.c
>>>>> +++ b/drivers/clocksource/arm_arch_timer.c
>>>>> @@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
>>>>>    	.mask	= CLOCKSOURCE_MASK(56),
>>>>>    };
>>>>>
>>>>> -static struct timecounter timecounter;
>>>>> +static struct arch_timer_kvm_info arch_timer_kvm_info;
>>>>
>>>> This structure is statically defined in this subsystem but not used in
>>>> this file and a couple of a accessors is added to let another subsystem
>>>> to access it.
>>>>
>>>> That sounds there is something wrong here with the design of the current
>>>> code, virt/phys are mixed.
>>>>
>>>> It isn't possible to split the virt/phys timer code respectively in
>>>> virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?
>>>
>>> No, that'd be the wrong thing to do. The kernel uses *either* the virt
>>> or phys timer depending on how it has been booted, and both counters are
>>> in use.
>>>
>>> What KVM (or any other hypervisor) needs from the timer subsystem is:
>>> - an interrupt (so that it can force a guest exit when the timer fires),
>>> - a way to convert the values programmed into the HW into a timer event
>>> (which is what the time counter structure is for).
>>>
>>> That allows the hypervisor to *emulate* a timer for the guest, and
>>> that's what virt/kvm/arm/arch_timer.c is all about. We have a clear
>>> separation of what is driving the HW vs what is emulating it, and I'm
>>> quite eager to preserve that.
>>>
>>>> At least, 'struct arch_timer_kvm_info' should belong to
>>>> virt/kvm/arm/arch_timer.c.
>>>
>>> At the cost of mandating separate storage in the arm_arch_timer driver.
>>> I do not find that much nicer, but if you prefer that, fine by me.
>>>
>> If arch_timer_kvm_info is declared in virt/kvm/arm/arch_timer.c, then
>> do you want to make it globally accessible and populated by this code or
>> make it static to the KVM code and populate it with accessor functions?
>
> That'd be the latter, as I'm really not fond of global data.
>
>> To me the natural thing is that the arch timer driver maintains data
>> about the device it drives, and consumers of that data can ask the arch
>> timer driver for the details.
>
> That was my approach too, and that's the way the code proposed by Julien
> works. Daniel seems to have a different take on it though.

Well, I'm not against Julien's changes. The arm_arch_timer is complex 
and I don't have all the knowledge for the virt side. So I am just 
asking if everything is clearly separated which seems to be the case 
regarding your previous email.

What sounds strange to me is we have a static global function which is 
not used (except at init time) by the timer and then we add accessors 
function to retrieve it. I would have expected arch_timer to pass a 
structure at init time to the timer driver and this one fills it. Then 
the arch timer can directly use its own structure.

Anyway, perhaps I am splitting hairs. So up to you if you want to keep 
the current approach.

   -- Daniel

Patch
diff mbox

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 5152b38..62bdfe7 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -468,11 +468,16 @@  static struct cyclecounter cyclecounter = {
 	.mask	= CLOCKSOURCE_MASK(56),
 };
 
-static struct timecounter timecounter;
+static struct arch_timer_kvm_info arch_timer_kvm_info;
+
+struct arch_timer_kvm_info *arch_timer_get_kvm_info(void)
+{
+	return &arch_timer_kvm_info;
+}
 
 struct timecounter *arch_timer_get_timecounter(void)
 {
-	return &timecounter;
+	return &arch_timer_kvm_info.timecounter;
 }
 
 static void __init arch_counter_register(unsigned type)
@@ -500,7 +505,8 @@  static void __init arch_counter_register(unsigned type)
 	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
 	cyclecounter.mult = clocksource_counter.mult;
 	cyclecounter.shift = clocksource_counter.shift;
-	timecounter_init(&timecounter, &cyclecounter, start_count);
+	timecounter_init(&arch_timer_kvm_info.timecounter,
+			 &cyclecounter, start_count);
 
 	/* 56 bits minimum, so we assume worst case rollover */
 	sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index 25d0914..9101ed6b 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -49,11 +49,16 @@  enum arch_timer_reg {
 
 #define ARCH_TIMER_EVT_STREAM_FREQ	10000	/* 100us */
 
+struct arch_timer_kvm_info {
+	struct timecounter timecounter;
+};
+
 #ifdef CONFIG_ARM_ARCH_TIMER
 
 extern u32 arch_timer_get_rate(void);
 extern u64 (*arch_timer_read_counter)(void);
 extern struct timecounter *arch_timer_get_timecounter(void);
+extern struct arch_timer_kvm_info *arch_timer_get_kvm_info(void);
 
 #else