From: Stephen Hemminger <stephen@networkplumber.org>
To: Wojciech Panfil <wojciech.panfil@intel.com>
Cc: <bruce.richardson@intel.com>, <pallavi.kadam@intel.com>,
<dev@dpdk.org>, <jacek.kalwas@intel.com>,
<konrad.sztyber@intel.com>, <dmitry.kozliuk@gmail.com>,
<roretzla@linux.microsoft.com>
Subject: Re: [PATCH] eal/alarm_cancel: Fix thread starvation
Date: Wed, 18 Sep 2024 09:06:10 -0700 [thread overview]
Message-ID: <20240918090610.1dcfb37c@hermes.local> (raw)
In-Reply-To: <20240918113906.64350-1-wojciech.panfil@intel.com>
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.
next prev parent reply other threads:[~2024-09-18 16:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-18 11:39 Wojciech Panfil
2024-09-18 16:06 ` Stephen Hemminger [this message]
-- strict thread matches above, loose matches on Subject: below --
2024-09-18 7:02 Wojciech Panfil
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