Re: [PATCH i-g-t 3/6] lib/xe/xe_sriov_admin: Lower priority before clearing timeslicing

On 8/18/2026 14:39, Marcin Bernatowicz wrote:
> Zero execution quantum and zero preemption timeout both mean infinity.
> A function left at a scheduling priority above LOW with infinite
> timeslicing may never be switched away from by GuC, which is a risky
> state that can be left via PAUSE/FLR.
>
> The restore helpers cleared execution quantum and preemption timeout
> first and only then dropped priority to LOW, transiting through exactly
> that state whenever a test had raised priority. This is reachable from
> xe_pmu, which restores defaults while VFs are still enabled, and from
> xe_sriov_admin_exit_cleanup_restore_sched_defaults() on abort or signal.
>
> Lower priority first, then clear execution quantum and preemption timeout.
>
> Assisted-by: Copilot:Claude-Opus-5
> Signed-off-by: Marcin Bernatowicz <[email protected]>
> Cc: Adam Miszczak <[email protected]>
> Cc: Jakub Kolakowski <[email protected]>
> Cc: Lukasz Laguna <[email protected]>

Reviewed-by: Lukasz Laguna <[email protected]>

> Cc: Michal Wajdeczko <[email protected]>
> ---
>   lib/xe/xe_sriov_admin.c | 32 ++++++++++++++++++++------------
>   1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/lib/xe/xe_sriov_admin.c b/lib/xe/xe_sriov_admin.c
> index b03e77b08..0433ddcfc 100644
> --- a/lib/xe/xe_sriov_admin.c
> +++ b/lib/xe/xe_sriov_admin.c
> @@ -547,6 +547,11 @@ void xe_sriov_admin_vf_stop(int pf_fd, unsigned int vf_num)
>    *
>    * Resets execution quantum, preemption timeout, and priority to driver defaults.
>    *
> + * Zero execution quantum and zero preemption timeout both mean infinity, so
> + * priority is lowered first. A function left at a priority above LOW with
> + * infinite timeslicing may never be switched away from by GuC, and can only be
> + * recovered by PAUSE/FLR.
> + *
>    * Returns: 0 on success or negative errno on error.
>    */
>   int __xe_sriov_admin_restore_sched_defaults(int pf_fd, unsigned int vf_num)
> @@ -554,6 +559,12 @@ int __xe_sriov_admin_restore_sched_defaults(int pf_fd, unsigned int vf_num)
>   	int ret_eq, ret_pt, ret_prio;
>   	int ret = 0;
>   
> +	ret_prio = __xe_sriov_admin_set_sched_priority(pf_fd, vf_num,
> +						       XE_SRIOV_SCHED_PRIORITY_LOW);
> +	igt_warn_on(ret_prio);
> +	if (!ret)
> +		ret = ret_prio;
> +
>   	ret_eq = __xe_sriov_admin_set_exec_quantum_ms(pf_fd, vf_num, 0);
>   	igt_warn_on(ret_eq);
>   	if (!ret)
> @@ -564,12 +575,6 @@ int __xe_sriov_admin_restore_sched_defaults(int pf_fd, unsigned int vf_num)
>   	if (!ret)
>   		ret = ret_pt;
>   
> -	ret_prio = __xe_sriov_admin_set_sched_priority(pf_fd, vf_num,
> -						       XE_SRIOV_SCHED_PRIORITY_LOW);
> -	igt_warn_on(ret_prio);
> -	if (!ret)
> -		ret = ret_prio;
> -
>   	return ret;
>   }
>   
> @@ -589,6 +594,9 @@ void xe_sriov_admin_restore_sched_defaults(int pf_fd, unsigned int vf_num)
>    *
>    * Resets PF and all VFs to driver default scheduling parameters.
>    *
> + * Priority is lowered before clearing timeslicing, see
> + * __xe_sriov_admin_restore_sched_defaults().
> + *
>    * Returns: 0 on success or negative errno on error.
>    */
>   int __xe_sriov_admin_bulk_restore_sched_defaults(int pf_fd)
> @@ -596,6 +604,12 @@ int __xe_sriov_admin_bulk_restore_sched_defaults(int pf_fd)
>   	int ret_eq, ret_pt, ret_prio;
>   	int ret = 0;
>   
> +	ret_prio = __xe_sriov_admin_bulk_set_sched_priority(pf_fd,
> +							    XE_SRIOV_SCHED_PRIORITY_LOW);
> +	igt_warn_on(ret_prio);
> +	if (!ret)
> +		ret = ret_prio;
> +
>   	ret_eq = __xe_sriov_admin_bulk_set_exec_quantum_ms(pf_fd, 0);
>   	igt_warn_on(ret_eq);
>   	if (!ret)
> @@ -606,12 +620,6 @@ int __xe_sriov_admin_bulk_restore_sched_defaults(int pf_fd)
>   	if (!ret)
>   		ret = ret_pt;
>   
> -	ret_prio = __xe_sriov_admin_bulk_set_sched_priority(pf_fd,
> -							    XE_SRIOV_SCHED_PRIORITY_LOW);
> -	igt_warn_on(ret_prio);
> -	if (!ret)
> -		ret = ret_prio;
> -
>   	return ret;
>   }
>