Re: [PATCH 4/4] task_work: use TIF_NOTIFY_SIGNAL if available

Jens Axboe
2020-10-14T09:19:45Z

On 10/13/20 5:50 PM, Thomas Gleixner wrote:
> On Thu, Oct 08 2020 at 09:27, Jens Axboe wrote:
>> +/*
>> + * TWA_SIGNAL signaling - use TIF_NOTIFY_SIGNAL, if available, as it's faster
>> + * than TIF_SIGPENDING as there's no dependency on ->sighand. The latter is
>> + * shared for threads, and can cause contention on sighand->lock. Even for
>> + * the non-threaded case TIF_NOTIFY_SIGNAL is more efficient, as no locking
>> + * or IRQ disabling is involved for notification (or running) purposes.
>> + */
>> +static void task_work_notify_signal(struct task_struct *task)
>> +{
>> +#ifdef TIF_NOTIFY_SIGNAL
>> + set_notify_signal(task);
>> +#else
>> + unsigned long flags;
>> +
>> + /*
>> + * Only grab the sighand lock if we don't already have some
>> + * task_work pending. This pairs with the smp_store_mb()
>> + * in get_signal(), see comment there.
>> + */
>> + if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
>> + lock_task_sighand(task, &flags)) {
>> + task->jobctl |= JOBCTL_TASK_WORK;
>> + signal_wake_up(task, 0);
>> + unlock_task_sighand(task, &flags);
>> + }
>> +#endif
>
> Same #ifdeffery comment as before.

Fixed up.

--
Jens Axboe