diff mbox series

device-drivers/cpufreq_boost: skip test on virtual machines

Message ID 20210623080157.26424-1-krzysztof.kozlowski@canonical.com
State New
Headers show
Series device-drivers/cpufreq_boost: skip test on virtual machines | expand

Commit Message

Krzysztof Kozlowski June 23, 2021, 8:01 a.m. UTC
Testing CPU frequency boost on a virtual machines is not reliable.  Even
if cpufreq driver reports boost frequencies, the underlying hypervisor
might decide otherwise.

For example on AWS x1e.xlarge instance (claimed to be running on Intel
Xeon E7 8880) under Xen hypervisor the test always fails:

    cpufreq_boost    0  TINFO  :  found 'intel_pstate' driver, sysfs knob '/sys/devices/system/cpu/intel_pstate/no_turbo'
    cpufreq_boost    0  TINFO  :  maximum speed is 3100000 KHz
    cpufreq_boost    0  TINFO  :  load CPU0 with boost enabled
    cpufreq_boost    0  TINFO  :  elapsed time is 1155 ms
    cpufreq_boost    0  TINFO  :  load CPU0 with boost disabled
    cpufreq_boost    0  TINFO  :  elapsed time is 1155 ms
    cpufreq_boost    1  TFAIL  :  cpufreq_boost.c:186: compare time spent with and without boost (-2%)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Krzysztof Kozlowski June 23, 2021, 8:11 a.m. UTC | #1
On 23/06/2021 10:01, Krzysztof Kozlowski wrote:
> Testing CPU frequency boost on a virtual machines is not reliable.  Even
> if cpufreq driver reports boost frequencies, the underlying hypervisor
> might decide otherwise.
> 
> For example on AWS x1e.xlarge instance (claimed to be running on Intel
> Xeon E7 8880) under Xen hypervisor the test always fails:
> 
>     cpufreq_boost    0  TINFO  :  found 'intel_pstate' driver, sysfs knob '/sys/devices/system/cpu/intel_pstate/no_turbo'
>     cpufreq_boost    0  TINFO  :  maximum speed is 3100000 KHz
>     cpufreq_boost    0  TINFO  :  load CPU0 with boost enabled
>     cpufreq_boost    0  TINFO  :  elapsed time is 1155 ms
>     cpufreq_boost    0  TINFO  :  load CPU0 with boost disabled
>     cpufreq_boost    0  TINFO  :  elapsed time is 1155 ms
>     cpufreq_boost    1  TFAIL  :  cpufreq_boost.c:186: compare time spent with and without boost (-2%)
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> ---
>  testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> index b9739db37cb7..67917b3fea25 100644
> --- a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> +++ b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> @@ -90,6 +90,9 @@ static void setup(void)
>  	unsigned int i;
>  	tst_require_root();
>  
> +	if (tst_is_virt(VIRT_ANY))
> +		tst_brkm(TCONF, NULL, "running in a virtual machine, overclock not reliably measureable");
> +
>  	for (i = 0; i < ARRAY_SIZE(cdrv); ++i) {
>  		fd = open(cdrv[i].file, O_RDWR);
>  		if (fd == -1)
> 

Optionally, under virtual machine the test failure could be converted to
accepted pass. This would still allow to test CPUfreq boosting
interface. Any preferences?

Best regards,
Krzysztof
Cyril Hrubis June 23, 2021, 11:38 a.m. UTC | #2
Hi!
> > diff --git a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> > index b9739db37cb7..67917b3fea25 100644
> > --- a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> > +++ b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
> > @@ -90,6 +90,9 @@ static void setup(void)
> >  	unsigned int i;
> >  	tst_require_root();
> >  
> > +	if (tst_is_virt(VIRT_ANY))
> > +		tst_brkm(TCONF, NULL, "running in a virtual machine, overclock not reliably measureable");
> > +
> >  	for (i = 0; i < ARRAY_SIZE(cdrv); ++i) {
> >  		fd = open(cdrv[i].file, O_RDWR);
> >  		if (fd == -1)
> > 
> 
> Optionally, under virtual machine the test failure could be converted to
> accepted pass. This would still allow to test CPUfreq boosting
> interface. Any preferences?

I wonder what is the likehood of actually dicovering a bug by writing to
the cpufreq boost file from within a VM, I guess that it's non-zero at
least.
Krzysztof Kozlowski June 23, 2021, 3:33 p.m. UTC | #3
On 23/06/2021 13:38, Cyril Hrubis wrote:
> Hi!
>>> diff --git a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
>>> index b9739db37cb7..67917b3fea25 100644
>>> --- a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
>>> +++ b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
>>> @@ -90,6 +90,9 @@ static void setup(void)
>>>  	unsigned int i;
>>>  	tst_require_root();
>>>  
>>> +	if (tst_is_virt(VIRT_ANY))
>>> +		tst_brkm(TCONF, NULL, "running in a virtual machine, overclock not reliably measureable");
>>> +
>>>  	for (i = 0; i < ARRAY_SIZE(cdrv); ++i) {
>>>  		fd = open(cdrv[i].file, O_RDWR);
>>>  		if (fd == -1)
>>>
>>
>> Optionally, under virtual machine the test failure could be converted to
>> accepted pass. This would still allow to test CPUfreq boosting
>> interface. Any preferences?
> 
> I wonder what is the likehood of actually dicovering a bug by writing to
> the cpufreq boost file from within a VM, I guess that it's non-zero at
> least.

It's a test of kernel interface and whether the driver accepts input via
sysfs... so not much of a real cpufreq test. Indeed maybe better to skip
the test explicitly instead of giving some false hopes that cpufreq is
being tested.


Best regards,
Krzysztof
diff mbox series

Patch

diff --git a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
index b9739db37cb7..67917b3fea25 100644
--- a/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
+++ b/testcases/kernel/device-drivers/cpufreq/cpufreq_boost.c
@@ -90,6 +90,9 @@  static void setup(void)
 	unsigned int i;
 	tst_require_root();
 
+	if (tst_is_virt(VIRT_ANY))
+		tst_brkm(TCONF, NULL, "running in a virtual machine, overclock not reliably measureable");
+
 	for (i = 0; i < ARRAY_SIZE(cdrv); ++i) {
 		fd = open(cdrv[i].file, O_RDWR);
 		if (fd == -1)