Re: [dpdk-dev] CPU hog & memory leak on FreeBSD

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

Hello,
	I can take a look if you can post the patch.

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Lewis Donzis
> Sent: Monday, August 3, 2020 2:43 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] CPU hog & memory leak on FreeBSD
> 
> Hello.
> 
> We've posted about this before, but I'm hoping to find someone willing to
> commit a patched version of lib/librte_eal/bsdapp/eal/eal_interrupts.c that
> corrects a memory leak and 100% CPU hog that is immediately noticeable
> with the i40e driver, at a minimum. We have modified this file to correct the
> problem, and would be happy to provide it back to whomever is a committer
> for this.
If you can send a patch, I can take a look.

> 
> The detailed explanation is:
> 
> Currently, s etting an alarm with rte_eal_alarm_set() registers an alarm
> interrupt by calling rte_intr_callback_register(), which links the callback
> function (eal_alarm_callback) onto a list for that source and sets up a one-
> shot timer via kevent. Setting additional alarms links them on to the
> alarm_list, but also calls rte_eal_alarm_set() again, which links the callback
> function onto the source callback list again.
> 
> When the alarm triggers and eal_alarm_callback() gets called, it goes down
> the list of pending alarms, calling as many callback functions as possible and
> removing each one from the list until it reaches one which has not yet expired.
> Once it's done, if alarm_list is not empty, it calls rte_intr_callback_register(),
> which then links yet another callback onto the interrupt source's list, thus
> creating an infinite loop.
> 
> The problem is that the source callback list grows infinitely under this
> condition (essentially, when more than one alarm is queued). However, the
> call is necessary in order to reset the kevent timer.
> 
> The proposed fix recognizes and leverages the fact that an alarm interrupt in
> FreeBSD should never have more than one callback on its list, so if
Is your fix applicable only for FreeBSD?

> rte_intr_callback_register() is called with an interrupt handle type of
> RTE_INTR_HANDLE_ALARM, and if such an interrupt type already has a non-
> empty list, then a new callback is not created, but the kevent timer is
> restarted properly.
> 
> A much simpler change is possible if we don't mind the overhead of allocating,
> filling-in, linking, de-linking, and freeing a callback unnecessarily. This
> proposed change makes every attempt to avoid that overhead.