Re: [dpdk-dev] [PATCH] eal: initialize alarms early

[Thomas Monjalon <thomas@monjalon.net>]

28/03/2019 11:43, Bruce Richardson:
> On Wed, Mar 27, 2019 at 11:42:40PM +0100, Thomas Monjalon wrote:
> > 27/03/2019 21:33, Stojaczyk, Dariusz:
> > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > > 26/03/2019 19:43, Darek Stojaczyk:
> > > > > We currently initialize rte_alarms after starting
> > > > > to listen for IPC hotplug requests, which gives
> > > > > us a data race window. Upon receiving such hotplug
> > > > > request we always try to set an alarm and this
> > > > > obviously doesn't work if the alarms weren't
> > > > > initialized yet.
> > > > >
> > > > > To fix it, we initialize alarms before starting
> > > > > to listen for IPC hotplug messages. Specifically,
> > > > > we move rte_eal_alarm_init() right after
> > > > > rte_eal_intr_init() as it makes some sense to
> > > > > keep those two close to each other.
> > > > 
> > > > I wonder which regression it will bring :)
> > > > The experience shows that we cannot touch this function
> > > > without introducing a regression. Please check twice.
> > > 
> > > Hah, ok - I'll check again the possible outcomes of this.
> > > 
> > > > 
> > > > > Fixes: 244d5130719c ("eal: enable hotplug on multi-process")
> > > > > Cc: Qi Zhang <qi.z.zhang@intel.com>
> > > > > Cc: Anatoly Burakov <anatoly.burakov@intel.com>
> > > > > Cc: stable@dpdk.org
> > > > >
> > > > > Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
> > > > > ---
> > > > >  lib/librte_eal/linux/eal/eal.c | 12 ++++++------
> > > > >  1 file changed, 6 insertions(+), 6 deletions(-)
> > > > 
> > > > You probably need to update the FreeBSD version too.
> > > > 
> > > 
> > > Oh, that I cannot do. First of all, in bsd code I don't see
> > > rte_mp_dev_hotplug_init() called anywhere, as if bsd
> > > did not listen for IPC hotplug messages at all and hence did
> > > not have any data race in this area. Second, I would be
> > > afraid to touch any bsd code as I'm not running any bsd
> > > system.
> > 
> > The problem is the consistency between OSes.
> > May you ask help here? Bruce is maintaining the FreeBSD side.
> > 
> I don't think we support IPC or hotplug on BSD, so I don't think this patch
> is relevant on the BSD side.

Yes, but then, the initialization order is different on Linux and BSD.
I'm thinking about consistency and maintenance ease.