Re: [igt-dev] [PATCH i-g-t] lib/xe/xe_query: Extern xe_supports_faults()

[Mauro Carvalho Chehab <mauro.chehab@linux.intel.com>]

On Thu, 23 Mar 2023 23:23:35 -0700
Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com> wrote:

> On Fri, Mar 24, 2023 at 07:12:46AM +0100, Mauro Carvalho Chehab wrote:
> >On Thu, 23 Mar 2023 22:02:53 -0700
> >Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com> wrote:
> >
> >> Do not check for supports_faults in xe_device_get() as
> >> it creates a VM in fault mode which prohibits creation
> >> of any other VM in non-fault mode until this fault mode
> >> VM is closed. This leads to test failures in multi threaded
> >> cases.
> >
> >Hmm...
> >
> >>
> >> Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
> >> ---
> >>  lib/xe/xe_query.c | 51 ++++++++++++++++++++++-------------------------
> >>  lib/xe/xe_query.h |  3 ---
> >>  2 files changed, 24 insertions(+), 30 deletions(-)
> >>
> >> diff --git a/lib/xe/xe_query.c b/lib/xe/xe_query.c
> >> index 183523280..dc91d59bc 100644
> >> --- a/lib/xe/xe_query.c
> >> +++ b/lib/xe/xe_query.c
> >> @@ -160,23 +160,6 @@ static uint32_t __mem_default_alignment(struct drm_xe_query_mem_usage *mem_usage
> >>  	return alignment;
> >>  }
> >>
> >> -static bool xe_check_supports_faults(int fd)
> >> -{
> >> -	bool supports_faults;
> >> -
> >> -	struct drm_xe_vm_create create = {
> >> -		.flags = DRM_XE_VM_CREATE_ASYNC_BIND_OPS |
> >> -			 DRM_XE_VM_CREATE_FAULT_MODE,
> >> -	};
> >> -
> >> -	supports_faults = !igt_ioctl(fd, DRM_IOCTL_XE_VM_CREATE, &create);
> >> -
> >> -	if (supports_faults)
> >> -		xe_vm_destroy(fd, create.vm_id);
> >
> >Weren't the VM supposed to be closed here?
> >
> 
> Yes, but before it does destroy the VM, some other thread can try
> to create a VM in non-fault mode and fail because we have created
> a fault mode VM here. This happens in multi-threaded test like
> xe_exec_threads.

Ok. Please add a note at the kernel-doc. Something like:

	/**
	 * xe_supports_faults:
	 * @fd: xe device fd
	 *
	 * Returns true if xe device @fd allows creating vm in fault mode otherwise
	 * false.
	 *
	 * Please note that, while this function is executed, no
	 * non-fault mode VMs can be created.  
	 */
	bool xe_supports_faults(int fd)

On Fri, 24 Mar 2023 06:53:52 +0000
Matthew Brost <matthew.brost@intel.com> wrote:

> On Thu, Mar 23, 2023 at 10:02:53PM -0700, Niranjana Vishwanathapura wrote:
>
> Just a general comment, we probably should report if the device supports
> faults via the device query IOCTL. Let me look into that (and a few
> other query issues) and post a RFC.

Agreed. Specially for ioctls like this that, which checking if a feature
is supported will change the driver's state machine, placing the
data into the query ioctl is a need.

Regards,
Mauro