Re: [PATCH] eal/alarm_cancel: Fix thread starvation

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 18 Sep 2024 13:39:06 +0200
Wojciech Panfil <wojciech.panfil@intel.com> wrote:

> Issue:
> Two threads:
> 
> - A, executing rte_eal_alarm_cancel,
> - B, executing eal_alarm_callback.
> 
> Such case can cause starvation of thread B. Please see that there is a
> small time window between lock and unlock in thread A, so thread B must
> be switched to within a very small time window, so that it can obtain
> the lock.
> 
> Solution to this problem is use sched_yield(), which puts current thread
> (A) at the end of thread execution priority queue and allows thread B to
> execute.
> 
> The issue can be observed e.g. on hot-pluggable device detach path.
> On such path, rte_alarm can used to check if DPDK has completed
> the detachment. Waiting for completion, rte_eal_alarm_cancel
> is called, while another thread periodically calls eal_alarm_callback
> causing the issue to occur.
> 
> Signed-off-by: Wojciech Panfil <wojciech.panfil@intel.com>

Make sense. Alarm is non-EAL thread, and so is hotplug.

Acked-by: Stephen Hemminger <stephen@networkplumber.org>

Does the timer_stop code have similar issues?
Probably only if users do unexpected things like
map multiple logical lcores to same CPU.