Hello,
On Wed, Sep 23, 2026 at 05:12:50PM +0100, Tvrtko Ursulin wrote:
> For use cases such as the DRM scheduler submitting work to the GPU on
> behalf of low latency userspace applications, where latter have sufficient
> privileges to have had successfully obtained realtime Vulkan global
> priority, competing with random background CPU load can create large
> latency spikes which gets in the way of a smooth user experience.
panthor's group_priority_permit() also allows realtime groups for DRM
master without CAP_SYS_NICE. What's the usage model there? Should DRM
master be enough to get RT workers?
> @@ -374,8 +374,9 @@ enum wq_flags {
> WQ_FREEZABLE = 1 << 2, /* freeze during suspend */
> WQ_MEM_RECLAIM = 1 << 3, /* may be used for memory reclaim */
> WQ_HIGHPRI = 1 << 4, /* high priority */
> - WQ_CPU_INTENSIVE = 1 << 5, /* cpu intensive workqueue */
> - WQ_SYSFS = 1 << 6, /* visible in sysfs, see
> workqueue_sysfs_register() */
> + WQ_RTPRI = 1 << 5, /* real-time priority, valid only
> with WQ_UNBOUND */
> + WQ_CPU_INTENSIVE = 1 << 6, /* cpu intensive workqueue */
> + WQ_SYSFS = 1 << 7, /* visible in sysfs, see
> workqueue_sysfs_register() */
Can we name it just WQ_RT? Also, I think WQ_RT is closer to WQ_BH. We can
reorder the flags later if that helps but for now can you just put it in an
empty slot?
> @@ -127,6 +127,7 @@ enum wq_internal_consts {
> */
> RESCUER_NICE_LEVEL = MIN_NICE,
> HIGHPRI_NICE_LEVEL = MIN_NICE,
> + RTPRI_NICE_LEVEL = MIN_NICE - 1,
Can we match the scheduler's representation instead by replacing
attrs->nice with attrs->prio which uses the same encoding as p->prio?
Normal pools would be NICE_TO_PRIO(nice) and WQ_RT pools would be in the RT
range. create_worker() would then do:
if (rt_prio(pool->attrs->prio))
sched_set_fifo_low(worker->task);
else
set_user_nice(worker->task, PRIO_TO_NICE(pool->attrs->prio));
> @@ -7606,7 +7626,10 @@ static ssize_t nice_show(struct device *dev, struct
> device_attribute *attr,
> int written;
>
> mutex_lock(&wq->mutex);
> - written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->attrs->nice);
> + if (wq->attrs->nice == RTPRI_NICE_LEVEL)
> + written = scnprintf(buf, PAGE_SIZE, "rt\n");
> + else
> + written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->attrs->nice);
Can you also show rt in pr_cont_pool_info() and tools/workqueue/wq_dump.py?
Thanks.
--
tejun
