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

[David Marchand <david.marchand@redhat.com>]

On Wed, Sep 25, 2024 at 9:34 PM 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>

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

Applied, thanks (and welcome) Wojciech.


-- 
David Marchand