[PATCH] Replace kvm io delay pv-ops with linux magic

[PATCH] Replace kvm io delay pv-ops with linux magic

[Alexander Graf]

Currently we use pv-ops to tell linux not to do anything on io_delay.

While the basic idea is good IMHO, I don't see why we would need pv-ops
for that. The io delay function already has a switch that can do nothing
if you're so inclined.

So here's a patch (stacked on top of the previous pv-ops series) that
removes the io delay pv-ops hook and just sets the native io delay
variable instead.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 arch/x86/Kconfig      |   14 --------------
 arch/x86/kernel/kvm.c |   16 +++-------------
 2 files changed, 3 insertions(+), 27 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 97d4f92..ebed686 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -527,20 +527,6 @@ config KVM_GUEST
 	  This option enables various optimizations for running under the KVM
 	  hypervisor.
 
-config KVM_IODELAY
-	bool "KVM IO-delay support"
-	depends on KVM_GUEST
-	select PARAVIRT_CPU
-	---help---
-	  Usually we wait for PIO access to complete. When inside KVM there's
-	  no need to do that, as we know that we're not going through a bus,
-	  but process PIO requests instantly.
-
-	  This option disables PIO waits, but drags in CPU-bound pv-ops. Thus
-	  you will probably get more speed loss than speedup using this option.
-
-	  If in doubt, say N.
-
 config KVM_MMU
 	bool "KVM PV MMU support"
 	depends on KVM_GUEST
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 7e0207f..be182e6 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -29,15 +29,6 @@
 #include <linux/hardirq.h>
 #include <asm/timer.h>
 
-#ifdef CONFIG_KVM_IODELAY
-/*
- * No need for any "IO delay" on KVM
- */
-static void kvm_io_delay(void)
-{
-}
-#endif  /* CONFIG_KVM_IODELAY */
-
 #ifdef CONFIG_KVM_MMU
 #define MMU_QUEUE_SIZE 1024
 
@@ -201,13 +192,12 @@ static void kvm_leave_lazy_mmu(void)
 
 static void __init paravirt_ops_setup(void)
 {
+	extern int io_delay_type;
 	pv_info.name = "KVM";
 	pv_info.paravirt_enabled = 1;
 
-#ifdef CONFIG_KVM_IODELAY
-	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
-		pv_cpu_ops.io_delay = kvm_io_delay;
-#endif
+	/* Disable IO delay */
+	io_delay_type = CONFIG_IO_DELAY_TYPE_NONE;
 
 #ifdef CONFIG_KVM_MMU
 	if (kvm_para_has_feature(KVM_FEATURE_MMU_OP)) {
-- 
1.6.0.2

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Jeremy Fitzhardinge]

On 11/18/09 20:56, Alexander Graf wrote:
> Currently we use pv-ops to tell linux not to do anything on io_delay.
>
> While the basic idea is good IMHO, I don't see why we would need pv-ops
> for that. The io delay function already has a switch that can do nothing
> if you're so inclined.
>
> So here's a patch (stacked on top of the previous pv-ops series) that
> removes the io delay pv-ops hook and just sets the native io delay
> variable instead.
>   

Can you just get rid of the io_delay op altogether?  If KVM doesn't need
it, then nobody does.

    J

> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  arch/x86/Kconfig      |   14 --------------
>  arch/x86/kernel/kvm.c |   16 +++-------------
>  2 files changed, 3 insertions(+), 27 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 97d4f92..ebed686 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -527,20 +527,6 @@ config KVM_GUEST
>  	  This option enables various optimizations for running under the KVM
>  	  hypervisor.
>  
> -config KVM_IODELAY
> -	bool "KVM IO-delay support"
> -	depends on KVM_GUEST
> -	select PARAVIRT_CPU
> -	---help---
> -	  Usually we wait for PIO access to complete. When inside KVM there's
> -	  no need to do that, as we know that we're not going through a bus,
> -	  but process PIO requests instantly.
> -
> -	  This option disables PIO waits, but drags in CPU-bound pv-ops. Thus
> -	  you will probably get more speed loss than speedup using this option.
> -
> -	  If in doubt, say N.
> -
>  config KVM_MMU
>  	bool "KVM PV MMU support"
>  	depends on KVM_GUEST
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 7e0207f..be182e6 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -29,15 +29,6 @@
>  #include <linux/hardirq.h>
>  #include <asm/timer.h>
>  
> -#ifdef CONFIG_KVM_IODELAY
> -/*
> - * No need for any "IO delay" on KVM
> - */
> -static void kvm_io_delay(void)
> -{
> -}
> -#endif  /* CONFIG_KVM_IODELAY */
> -
>  #ifdef CONFIG_KVM_MMU
>  #define MMU_QUEUE_SIZE 1024
>  
> @@ -201,13 +192,12 @@ static void kvm_leave_lazy_mmu(void)
>  
>  static void __init paravirt_ops_setup(void)
>  {
> +	extern int io_delay_type;
>  	pv_info.name = "KVM";
>  	pv_info.paravirt_enabled = 1;
>  
> -#ifdef CONFIG_KVM_IODELAY
> -	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
> -		pv_cpu_ops.io_delay = kvm_io_delay;
> -#endif
> +	/* Disable IO delay */
> +	io_delay_type = CONFIG_IO_DELAY_TYPE_NONE;
>  
>  #ifdef CONFIG_KVM_MMU
>  	if (kvm_para_has_feature(KVM_FEATURE_MMU_OP)) {
>   

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Alexander Graf]

Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:

> On 11/18/09 20:56, Alexander Graf wrote:
>> Currently we use pv-ops to tell linux not to do anything on io_delay.
>>
>> While the basic idea is good IMHO, I don't see why we would need pv- 
>> ops
>> for that. The io delay function already has a switch that can do  
>> nothing
>> if you're so inclined.
>>
>> So here's a patch (stacked on top of the previous pv-ops series) that
>> removes the io delay pv-ops hook and just sets the native io delay
>> variable instead.
>>
>
> Can you just get rid of the io_delay op altogether?  If KVM doesn't  
> need
> it, then nobody does.

Sure, can do. That'd be a separate patch though.

Alex

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Jeremy Fitzhardinge]

On 11/20/09 07:58, Alexander Graf wrote:
>
> Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:
>
>> On 11/18/09 20:56, Alexander Graf wrote:
>>> Currently we use pv-ops to tell linux not to do anything on io_delay.
>>>
>>> While the basic idea is good IMHO, I don't see why we would need pv-ops
>>> for that. The io delay function already has a switch that can do
>>> nothing
>>> if you're so inclined.
>>>
>>> So here's a patch (stacked on top of the previous pv-ops series) that
>>> removes the io delay pv-ops hook and just sets the native io delay
>>> variable instead.
>>>
>>
>> Can you just get rid of the io_delay op altogether?  If KVM doesn't need
>> it, then nobody does.
>
> Sure, can do. That'd be a separate patch though.

Yep.  A patch each for VMI and Xen to remove the dependency, and a final
patch to remove the op.  Hm, looks like VMI has a specific ROM call for
io_delay; I wonder what it does.

    J

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Alexander Graf]

On 20.11.2009, at 02:54, Jeremy Fitzhardinge wrote:

> On 11/20/09 07:58, Alexander Graf wrote:
>>
>> Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:
>>
>>> On 11/18/09 20:56, Alexander Graf wrote:
>>>> Currently we use pv-ops to tell linux not to do anything on  
>>>> io_delay.
>>>>
>>>> While the basic idea is good IMHO, I don't see why we would need  
>>>> pv-ops
>>>> for that. The io delay function already has a switch that can do
>>>> nothing
>>>> if you're so inclined.
>>>>
>>>> So here's a patch (stacked on top of the previous pv-ops series)  
>>>> that
>>>> removes the io delay pv-ops hook and just sets the native io delay
>>>> variable instead.
>>>>
>>>
>>> Can you just get rid of the io_delay op altogether?  If KVM  
>>> doesn't need
>>> it, then nobody does.
>>
>> Sure, can do. That'd be a separate patch though.
>
> Yep.  A patch each for VMI and Xen to remove the dependency, and a  
> final
> patch to remove the op.  Hm, looks like VMI has a specific ROM call  
> for
> io_delay; I wonder what it does.

Oh so it's actually using it? Feel like doing the removal then? I  
don't really want to mess with VMI code :-)

Alex

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Jeremy Fitzhardinge]

On 11/20/09 09:59, Alexander Graf wrote:
>
> On 20.11.2009, at 02:54, Jeremy Fitzhardinge wrote:
>
>> On 11/20/09 07:58, Alexander Graf wrote:
>>>
>>> Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:
>>>
>>>> On 11/18/09 20:56, Alexander Graf wrote:
>>>>> Currently we use pv-ops to tell linux not to do anything on io_delay.
>>>>>
>>>>> While the basic idea is good IMHO, I don't see why we would need
>>>>> pv-ops
>>>>> for that. The io delay function already has a switch that can do
>>>>> nothing
>>>>> if you're so inclined.
>>>>>
>>>>> So here's a patch (stacked on top of the previous pv-ops series) that
>>>>> removes the io delay pv-ops hook and just sets the native io delay
>>>>> variable instead.
>>>>>
>>>>
>>>> Can you just get rid of the io_delay op altogether?  If KVM doesn't
>>>> need
>>>> it, then nobody does.
>>>
>>> Sure, can do. That'd be a separate patch though.
>>
>> Yep.  A patch each for VMI and Xen to remove the dependency, and a final
>> patch to remove the op.  Hm, looks like VMI has a specific ROM call for
>> io_delay; I wonder what it does.
>
> Oh so it's actually using it? Feel like doing the removal then? I
> don't really want to mess with VMI code :-)

I would post the patch and see if Alok naks it.  But I somehow doubt
vmware is doing anything profound with that call.

    J

Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Alok Kataria]

On Thu, 2009-11-19 at 18:08 -0800, Jeremy Fitzhardinge wrote:
> On 11/20/09 09:59, Alexander Graf wrote:
> >
> > On 20.11.2009, at 02:54, Jeremy Fitzhardinge wrote:
> >
> >> On 11/20/09 07:58, Alexander Graf wrote:
> >>>
> >>> Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:
> >>>
> >>>> On 11/18/09 20:56, Alexander Graf wrote:
> >>>>> Currently we use pv-ops to tell linux not to do anything on io_delay.
> >>>>>
> >>>>> While the basic idea is good IMHO, I don't see why we would need
> >>>>> pv-ops
> >>>>> for that. The io delay function already has a switch that can do
> >>>>> nothing
> >>>>> if you're so inclined.
> >>>>>
> >>>>> So here's a patch (stacked on top of the previous pv-ops series) that
> >>>>> removes the io delay pv-ops hook and just sets the native io delay
> >>>>> variable instead.
> >>>>>
> >>>>
> >>>> Can you just get rid of the io_delay op altogether?  If KVM doesn't
> >>>> need
> >>>> it, then nobody does.
> >>>
> >>> Sure, can do. That'd be a separate patch though.
> >>
> >> Yep.  A patch each for VMI and Xen to remove the dependency, and a final
> >> patch to remove the op.  Hm, looks like VMI has a specific ROM call for
> >> io_delay; I wonder what it does.
> >
> > Oh so it's actually using it? Feel like doing the removal then? I
> > don't really want to mess with VMI code :-)
> 
> I would post the patch and see if Alok naks it.  But I somehow doubt
> vmware is doing anything profound with that call.
> 

Yeah removing it is fine with me. That call is just a no-op anyways,
and, if there are other ways for avoiding the IO delay cost we can use
that one too.

Alok