virt_vtimer_save is calculating the new time for the vtimer in:
"v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
- boot_count".
In this formula, "cval + offset" might cause uint64_t overflow.
Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
v->arch.virt_timer.cval" can reduce the possibility of overflow, and
"arch.virt_timer_base.offset - boot_count" will be always the same,
which has been caculated in domain_vtimer_init. Introduce a new field
vtimer_offset.nanoseconds to store this value for arm in struct
arch_domain, so we can use it directly and extra caclulations can be
avoided.

This patch is enlightened from [1].

Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>

[1] https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg123139.htm
---
xen/arch/arm/include/asm/domain.h | 4 ++++
 xen/arch/arm/vtimer.c             | 6 ++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/include/asm/domain.h b/xen/arch/arm/include/asm/domain.h
index ed63c2b6f9..94fe5b6444 100644
--- a/xen/arch/arm/include/asm/domain.h
+++ b/xen/arch/arm/include/asm/domain.h
@@ -73,6 +73,10 @@ struct arch_domain
         uint64_t offset;
     } virt_timer_base;
 
+    struct {
+        int64_t nanoseconds;
+    } vtimer_offset;
+
     struct vgic_dist vgic;
 
     struct vuart {
diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index 6b78fea77d..54161e5fea 100644
--- a/xen/arch/arm/vtimer.c
+++ b/xen/arch/arm/vtimer.c
@@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct xen_arch_domainconfig *config)
 {
     d->arch.virt_timer_base.offset = get_cycles();
     d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
+    d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;
     do_div(d->time_offset.seconds, 1000000000);
 
     config->clock_frequency = timer_dt_clock_frequency;
@@ -144,8 +145,9 @@ void virt_timer_save(struct vcpu *v)
     if ( (v->arch.virt_timer.ctl & CNTx_CTL_ENABLE) &&
          !(v->arch.virt_timer.ctl & CNTx_CTL_MASK))
     {
-        set_timer(&v->arch.virt_timer.timer, ticks_to_ns(v->arch.virt_timer.cval +
-                  v->domain->arch.virt_timer_base.offset - boot_count));
+        set_timer(&v->arch.virt_timer.timer,
+                  v->domain->arch.vtimer_offset.nanoseconds +
+                  ticks_to_ns(v->arch.virt_timer.cval));
     }
 }
 
-- 
2.25.1

Hi Jiami

Title: s/caclulations/calculations/

However, I think the title should mention the overflow rather than the 
extra calculations. The former is more important the latter.

On 27/06/2022 03:58, Jiamei Xie wrote:
> virt_vtimer_save is calculating the new time for the vtimer in:
> "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> - boot_count".
> In this formula, "cval + offset" might cause uint64_t overflow.
> Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
> v->arch.virt_timer.cval" can reduce the possibility of overflow

This read strange to me. We want to remove the overflow completely not 
reducing it. The overflow is completely removed by converting the 
"offset - bount_count" to ns upfront.

AFAICT, the commit message doesn't explain that.

> , and
> "arch.virt_timer_base.offset - boot_count" will be always the same,
> which has been caculated in domain_vtimer_init. Introduce a new field
> vtimer_offset.nanoseconds to store this value for arm in struct
> arch_domain, so we can use it directly and extra caclulations can be
> avoided.
> 
> This patch is enlightened from [1].
> 
> Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>
> 
> [1] https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg123139.htm

This link doesn't work. But I would personally remove it from the commit 
message (or add ---) because it doesn't bring value (this patch looks 
like a v2 to me).

> ---
> xen/arch/arm/include/asm/domain.h | 4 ++++
>   xen/arch/arm/vtimer.c             | 6 ++++--
>   2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/domain.h b/xen/arch/arm/include/asm/domain.h
> index ed63c2b6f9..94fe5b6444 100644
> --- a/xen/arch/arm/include/asm/domain.h
> +++ b/xen/arch/arm/include/asm/domain.h
> @@ -73,6 +73,10 @@ struct arch_domain
>           uint64_t offset;
>       } virt_timer_base;
>   
> +    struct {
> +        int64_t nanoseconds;

This should be s_time_t to match the argument of set_timer() and return 
of ticks_to_ns().

> +    } vtimer_offset;

Why are you adding a new structure rather than re-using virt_timer_base?

> +
>       struct vgic_dist vgic;
>   
>       struct vuart {
> diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
> index 6b78fea77d..54161e5fea 100644
> --- a/xen/arch/arm/vtimer.c
> +++ b/xen/arch/arm/vtimer.c
> @@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct xen_arch_domainconfig *config)
>   {
>       d->arch.virt_timer_base.offset = get_cycles();
>       d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
> +    d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;

Hmmm... I find odd to assign a field "nanoseconds" to "seconds". I would 
suggest to re-order so you first set nanoseconds and then set seconds.

This will make more obvious that this is not a mistake and "seconds" 
will be closer to the do_div() below.

>       do_div(d->time_offset.seconds, 1000000000);
>   
>       config->clock_frequency = timer_dt_clock_frequency;
> @@ -144,8 +145,9 @@ void virt_timer_save(struct vcpu *v)
>       if ( (v->arch.virt_timer.ctl & CNTx_CTL_ENABLE) &&
>            !(v->arch.virt_timer.ctl & CNTx_CTL_MASK))
>       {
> -        set_timer(&v->arch.virt_timer.timer, ticks_to_ns(v->arch.virt_timer.cval +
> -                  v->domain->arch.virt_timer_base.offset - boot_count));
> +        set_timer(&v->arch.virt_timer.timer,
> +                  v->domain->arch.vtimer_offset.nanoseconds +
> +                  ticks_to_ns(v->arch.virt_timer.cval));
>       }
>   }
>   

Cheers,

-- 
Julien Grall

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: 2022年6月27日 18:36
> To: Jiamei Xie <Jiamei.Xie@arm.com>; xen-devel@lists.xenproject.org
> Cc: Stefano Stabellini <sstabellini@kernel.org>; Bertrand Marquis
> <Bertrand.Marquis@arm.com>; Volodymyr Babchuk
> <Volodymyr_Babchuk@epam.com>; Wei Chen <Wei.Chen@arm.com>
> Subject: Re: [PATCH] xen/arm: avoid extra caclulations when setting vtimer
> in context switch
> 
> Hi Jiami
> 
> Title: s/caclulations/calculations/
> 
> However, I think the title should mention the overflow rather than the
> extra calculations. The former is more important the latter.
> 
I will change the title to " xen/arm: avoid overflow when setting vtimer in context switch"

> On 27/06/2022 03:58, Jiamei Xie wrote:
> > virt_vtimer_save is calculating the new time for the vtimer in:
> > "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> > - boot_count".
> > In this formula, "cval + offset" might cause uint64_t overflow.
> > Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
> > v->arch.virt_timer.cval" can reduce the possibility of overflow
> 
> This read strange to me. We want to remove the overflow completely not
> reducing it. The overflow is completely removed by converting the
> "offset - bount_count" to ns upfront.
> 
> AFAICT, the commit message doesn't explain that.
Thanks for pointing out that. How about putting the commit message like the below:
    xen/arm: avoid overflow when setting vtimer in context switch

    virt_vtimer_save is calculating the new time for the vtimer in:
    "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
    - boot_count".
    In this formula, "cval + offset" might cause uint64_t overflow.
    Changing it to "ticks_to_ns(v->domain->arch.virt_timer_base.offset -
    boot_count) + ticks_to_ns(v->arch.virt_timer.cval)" can avoid overflow,
    and "ticks_to_ns(arch.virt_timer_base.offset - boot_count)" will be
    always the same, which has been caculated in domain_vtimer_init.
    Introduce a new field virt_timer_base.nanoseconds to store this value
    for arm in struct arch_domain, so we can use it directly.
> 
> > , and
> > "arch.virt_timer_base.offset - boot_count" will be always the same,
> > which has been caculated in domain_vtimer_init. Introduce a new field
> > vtimer_offset.nanoseconds to store this value for arm in struct
> > arch_domain, so we can use it directly and extra caclulations can be
> > avoided.
> >
> > This patch is enlightened from [1].
> >
> > Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>
> >
> > [1] https://www.mail-archive.com/xen-
> devel@lists.xenproject.org/msg123139.htm
> 
> This link doesn't work. But I would personally remove it from the commit
> message (or add ---) because it doesn't bring value (this patch looks
> like a v2 to me).
Sorry, a 'l' is missing at the end of the link.  The link is  https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg123139.html .
I will put it after --- in v3.
> 
> > ---
> > xen/arch/arm/include/asm/domain.h | 4 ++++
> >   xen/arch/arm/vtimer.c             | 6 ++++--
> >   2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/arch/arm/include/asm/domain.h
> b/xen/arch/arm/include/asm/domain.h
> > index ed63c2b6f9..94fe5b6444 100644
> > --- a/xen/arch/arm/include/asm/domain.h
> > +++ b/xen/arch/arm/include/asm/domain.h
> > @@ -73,6 +73,10 @@ struct arch_domain
> >           uint64_t offset;
> >       } virt_timer_base;
> >
> > +    struct {
> > +        int64_t nanoseconds;
> 
> This should be s_time_t to match the argument of set_timer() and return
> of ticks_to_ns().
> 
> > +    } vtimer_offset;
> 
> Why are you adding a new structure rather than re-using virt_timer_base?
Sure, I'll add this field in virt_timer_base.
     struct {
         uint64_t offset;
         s_time_t nanoseconds;
     } virt_timer_base;
> 
> > +
> >       struct vgic_dist vgic;
> >
> >       struct vuart {
> > diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
> > index 6b78fea77d..54161e5fea 100644
> > --- a/xen/arch/arm/vtimer.c
> > +++ b/xen/arch/arm/vtimer.c
> > @@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct
> xen_arch_domainconfig *config)
> >   {
> >       d->arch.virt_timer_base.offset = get_cycles();
> >       d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset -
> boot_count);
> > +    d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;
> 
> Hmmm... I find odd to assign a field "nanoseconds" to "seconds". I would
> suggest to re-order so you first set nanoseconds and then set seconds.
> 
> This will make more obvious that this is not a mistake and "seconds"
> will be closer to the do_div() below.
Is it ok to remove do_div and write like below?
    d->arch.virt_timer_base.nanoseconds =
        ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
    d->time_offset.seconds = d->arch.virt_timer_base.nanoseconds /
                              1000000000;

Best wishes
Jiamei Xie


> 
> >       do_div(d->time_offset.seconds, 1000000000);
> >
> >       config->clock_frequency = timer_dt_clock_frequency;
> > @@ -144,8 +145,9 @@ void virt_timer_save(struct vcpu *v)
> >       if ( (v->arch.virt_timer.ctl & CNTx_CTL_ENABLE) &&
> >            !(v->arch.virt_timer.ctl & CNTx_CTL_MASK))
> >       {
> > -        set_timer(&v->arch.virt_timer.timer, ticks_to_ns(v-
> >arch.virt_timer.cval +
> > -                  v->domain->arch.virt_timer_base.offset - boot_count));
> > +        set_timer(&v->arch.virt_timer.timer,
> > +                  v->domain->arch.vtimer_offset.nanoseconds +
> > +                  ticks_to_ns(v->arch.virt_timer.cval));
> >       }
> >   }
> >
> 
> Cheers,
> 
> --
> Julien Grall

Hi Jiamei,

> On 28 Jun 2022, at 07:35, Jiamei Xie <Jiamei.Xie@arm.com> wrote:
> 
> Hi Julien,
> 
>> -----Original Message-----
>> From: Julien Grall <julien@xen.org>
>> Sent: 2022年6月27日 18:36
>> To: Jiamei Xie <Jiamei.Xie@arm.com>; xen-devel@lists.xenproject.org
>> Cc: Stefano Stabellini <sstabellini@kernel.org>; Bertrand Marquis
>> <Bertrand.Marquis@arm.com>; Volodymyr Babchuk
>> <Volodymyr_Babchuk@epam.com>; Wei Chen <Wei.Chen@arm.com>
>> Subject: Re: [PATCH] xen/arm: avoid extra caclulations when setting vtimer
>> in context switch
>> 
>> Hi Jiami
>> 
>> Title: s/caclulations/calculations/
>> 
>> However, I think the title should mention the overflow rather than the
>> extra calculations. The former is more important the latter.
>> 
> I will change the title to " xen/arm: avoid overflow when setting vtimer in context switch"
> 
>> On 27/06/2022 03:58, Jiamei Xie wrote:
>>> virt_vtimer_save is calculating the new time for the vtimer in:
>>> "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
>>> - boot_count".
>>> In this formula, "cval + offset" might cause uint64_t overflow.
>>> Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
>>> v->arch.virt_timer.cval" can reduce the possibility of overflow
>> 
>> This read strange to me. We want to remove the overflow completely not
>> reducing it. The overflow is completely removed by converting the
>> "offset - bount_count" to ns upfront.
>> 
>> AFAICT, the commit message doesn't explain that.
> Thanks for pointing out that. How about putting the commit message like the below:
> xen/arm: avoid overflow when setting vtimer in context switch
> 
> virt_vtimer_save is calculating the new time for the vtimer in:
> "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> - boot_count".
> In this formula, "cval + offset" might cause uint64_t overflow.
> Changing it to "ticks_to_ns(v->domain->arch.virt_timer_base.offset -
> boot_count) + ticks_to_ns(v->arch.virt_timer.cval)" can avoid overflow,
> and "ticks_to_ns(arch.virt_timer_base.offset - boot_count)" will be
> always the same, which has been caculated in domain_vtimer_init.
> Introduce a new field virt_timer_base.nanoseconds to store this value
> for arm in struct arch_domain, so we can use it directly.
>> 
>>> , and
>>> "arch.virt_timer_base.offset - boot_count" will be always the same,
>>> which has been caculated in domain_vtimer_init. Introduce a new field
>>> vtimer_offset.nanoseconds to store this value for arm in struct
>>> arch_domain, so we can use it directly and extra caclulations can be
>>> avoided.
>>> 
>>> This patch is enlightened from [1].
>>> 
>>> Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>
>>> 
>>> [1] https://www.mail-archive.com/xen-
>> devel@lists.xenproject.org/msg123139.htm
>> 
>> This link doesn't work. But I would personally remove it from the commit
>> message (or add ---) because it doesn't bring value (this patch looks
>> like a v2 to me).
> Sorry, a 'l' is missing at the end of the link. The link is https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg123139.html .
> I will put it after --- in v3.
>> 
>>> ---
>>> xen/arch/arm/include/asm/domain.h | 4 ++++
>>> xen/arch/arm/vtimer.c | 6 ++++--
>>> 2 files changed, 8 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/xen/arch/arm/include/asm/domain.h
>> b/xen/arch/arm/include/asm/domain.h
>>> index ed63c2b6f9..94fe5b6444 100644
>>> --- a/xen/arch/arm/include/asm/domain.h
>>> +++ b/xen/arch/arm/include/asm/domain.h
>>> @@ -73,6 +73,10 @@ struct arch_domain
>>> uint64_t offset;
>>> } virt_timer_base;
>>> 
>>> + struct {
>>> + int64_t nanoseconds;
>> 
>> This should be s_time_t to match the argument of set_timer() and return
>> of ticks_to_ns().
>> 
>>> + } vtimer_offset;
>> 
>> Why are you adding a new structure rather than re-using virt_timer_base?
> Sure, I'll add this field in virt_timer_base.
> struct {
> uint64_t offset;
> s_time_t nanoseconds;
> } virt_timer_base;
>> 
>>> +
>>> struct vgic_dist vgic;
>>> 
>>> struct vuart {
>>> diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
>>> index 6b78fea77d..54161e5fea 100644
>>> --- a/xen/arch/arm/vtimer.c
>>> +++ b/xen/arch/arm/vtimer.c
>>> @@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct
>> xen_arch_domainconfig *config)
>>> {
>>> d->arch.virt_timer_base.offset = get_cycles();
>>> d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset -
>> boot_count);
>>> + d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;
>> 
>> Hmmm... I find odd to assign a field "nanoseconds" to "seconds". I would
>> suggest to re-order so you first set nanoseconds and then set seconds.
>> 
>> This will make more obvious that this is not a mistake and "seconds"
>> will be closer to the do_div() below.
> Is it ok to remove do_div and write like below?
> d->arch.virt_timer_base.nanoseconds =
> ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
> d->time_offset.seconds = d->arch.virt_timer_base.nanoseconds /
> 1000000000;

The implementation must use do_div to properly handle the division from a
64bit by a 32bit on arm32 otherwise the code will be a lot slower.

Cheers
Bertrand

Hi Bertrand,

> -----Original Message-----
> From: Bertrand Marquis <Bertrand.Marquis@arm.com>
> Sent: 2022年6月28日 15:29
> To: Jiamei Xie <Jiamei.Xie@arm.com>
> Cc: Julien Grall <julien@xen.org>; xen-devel@lists.xenproject.org; Stefano
> Stabellini <sstabellini@kernel.org>; Volodymyr Babchuk
> <Volodymyr_Babchuk@epam.com>; Wei Chen <Wei.Chen@arm.com>
> Subject: Re: [PATCH] xen/arm: avoid extra caclulations when setting vtimer
> in context switch
> 
> Hi Jiamei,
> 
> > On 28 Jun 2022, at 07:35, Jiamei Xie <Jiamei.Xie@arm.com> wrote:
> >
> > Hi Julien,
> >
> >> -----Original Message-----
> >> From: Julien Grall <julien@xen.org>
> >> Sent: 2022年6月27日 18:36
> >> To: Jiamei Xie <Jiamei.Xie@arm.com>; xen-devel@lists.xenproject.org
> >> Cc: Stefano Stabellini <sstabellini@kernel.org>; Bertrand Marquis
> >> <Bertrand.Marquis@arm.com>; Volodymyr Babchuk
> >> <Volodymyr_Babchuk@epam.com>; Wei Chen <Wei.Chen@arm.com>
> >> Subject: Re: [PATCH] xen/arm: avoid extra caclulations when setting
> vtimer
> >> in context switch
> >>
> >> Hi Jiami
> >>
> >> Title: s/caclulations/calculations/
> >>
> >> However, I think the title should mention the overflow rather than the
> >> extra calculations. The former is more important the latter.
> >>
> > I will change the title to " xen/arm: avoid overflow when setting vtimer in
> context switch"
> >
> >> On 27/06/2022 03:58, Jiamei Xie wrote:
> >>> virt_vtimer_save is calculating the new time for the vtimer in:
> >>> "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> >>> - boot_count".
> >>> In this formula, "cval + offset" might cause uint64_t overflow.
> >>> Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
> >>> v->arch.virt_timer.cval" can reduce the possibility of overflow
> >>
> >> This read strange to me. We want to remove the overflow completely not
> >> reducing it. The overflow is completely removed by converting the
> >> "offset - bount_count" to ns upfront.
> >>
> >> AFAICT, the commit message doesn't explain that.
> > Thanks for pointing out that. How about putting the commit message like
> the below:
> > xen/arm: avoid overflow when setting vtimer in context switch
> >
> > virt_vtimer_save is calculating the new time for the vtimer in:
> > "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> > - boot_count".
> > In this formula, "cval + offset" might cause uint64_t overflow.
> > Changing it to "ticks_to_ns(v->domain->arch.virt_timer_base.offset -
> > boot_count) + ticks_to_ns(v->arch.virt_timer.cval)" can avoid overflow,
> > and "ticks_to_ns(arch.virt_timer_base.offset - boot_count)" will be
> > always the same, which has been caculated in domain_vtimer_init.
> > Introduce a new field virt_timer_base.nanoseconds to store this value
> > for arm in struct arch_domain, so we can use it directly.
> >>
> >>> , and
> >>> "arch.virt_timer_base.offset - boot_count" will be always the same,
> >>> which has been caculated in domain_vtimer_init. Introduce a new field
> >>> vtimer_offset.nanoseconds to store this value for arm in struct
> >>> arch_domain, so we can use it directly and extra caclulations can be
> >>> avoided.
> >>>
> >>> This patch is enlightened from [1].
> >>>
> >>> Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>
> >>>
> >>> [1] https://www.mail-archive.com/xen-
> >> devel@lists.xenproject.org/msg123139.htm
> >>
> >> This link doesn't work. But I would personally remove it from the commit
> >> message (or add ---) because it doesn't bring value (this patch looks
> >> like a v2 to me).
> > Sorry, a 'l' is missing at the end of the link. The link is https://www.mail-
> archive.com/xen-devel@lists.xenproject.org/msg123139.html .
> > I will put it after --- in v3.
> >>
> >>> ---
> >>> xen/arch/arm/include/asm/domain.h | 4 ++++
> >>> xen/arch/arm/vtimer.c | 6 ++++--
> >>> 2 files changed, 8 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/xen/arch/arm/include/asm/domain.h
> >> b/xen/arch/arm/include/asm/domain.h
> >>> index ed63c2b6f9..94fe5b6444 100644
> >>> --- a/xen/arch/arm/include/asm/domain.h
> >>> +++ b/xen/arch/arm/include/asm/domain.h
> >>> @@ -73,6 +73,10 @@ struct arch_domain
> >>> uint64_t offset;
> >>> } virt_timer_base;
> >>>
> >>> + struct {
> >>> + int64_t nanoseconds;
> >>
> >> This should be s_time_t to match the argument of set_timer() and return
> >> of ticks_to_ns().
> >>
> >>> + } vtimer_offset;
> >>
> >> Why are you adding a new structure rather than re-using virt_timer_base?
> > Sure, I'll add this field in virt_timer_base.
> > struct {
> > uint64_t offset;
> > s_time_t nanoseconds;
> > } virt_timer_base;
> >>
> >>> +
> >>> struct vgic_dist vgic;
> >>>
> >>> struct vuart {
> >>> diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
> >>> index 6b78fea77d..54161e5fea 100644
> >>> --- a/xen/arch/arm/vtimer.c
> >>> +++ b/xen/arch/arm/vtimer.c
> >>> @@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct
> >> xen_arch_domainconfig *config)
> >>> {
> >>> d->arch.virt_timer_base.offset = get_cycles();
> >>> d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset -
> >> boot_count);
> >>> + d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;
> >>
> >> Hmmm... I find odd to assign a field "nanoseconds" to "seconds". I would
> >> suggest to re-order so you first set nanoseconds and then set seconds.
> >>
> >> This will make more obvious that this is not a mistake and "seconds"
> >> will be closer to the do_div() below.
> > Is it ok to remove do_div and write like below?
> > d->arch.virt_timer_base.nanoseconds =
> > ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
> > d->time_offset.seconds = d->arch.virt_timer_base.nanoseconds /
> > 1000000000;
> 
> The implementation must use do_div to properly handle the division from a
> 64bit by a 32bit on arm32 otherwise the code will be a lot slower.

Thanks for your explanation for this. I will keep the do_div. 

Best wishes
Jiamei Xie


> 
> Cheers
> Bertrand
>