[PATCH v2] net/pcap: fix timeout of stopping device

[Zhou, YidingX]

> -----Original Message-----
> From: Zhou, YidingX <yidingx.zhou at intel.com>
> Sent: Wednesday, September 21, 2022 3:15 PM
> To: Stephen Hemminger <stephen at networkplumber.org>; Zhang, Qi Z
> <qi.z.zhang at intel.com>
> Cc: dev at dpdk.org; Burakov, Anatoly <anatoly.burakov at intel.com>; He,
> Xingguang <xingguang.he at intel.com>; stable at dpdk.org
> Subject: RE: [PATCH v2] net/pcap: fix timeout of stopping device
> 
> 
> 
> > -----Original Message-----
> > From: Stephen Hemminger <mailto:stephen at networkplumber.org>
> > Sent: Tuesday, September 6, 2022 10:58 PM
> > To: Zhou, YidingX <mailto:yidingx.zhou at intel.com>
> > Cc: mailto:dev at dpdk.org; Zhang, Qi Z <mailto:qi.z.zhang at intel.com>; Burakov, Anatoly
> > <mailto:anatoly.burakov at intel.com>; He, Xingguang <mailto:xingguang.he at intel.com>;
> > mailto:stable at dpdk.org
> > Subject: Re: [PATCH v2] net/pcap: fix timeout of stopping device
> >
> > On Tue,  6 Sep 2022 16:05:11 +0800
> > Yiding Zhou <mailto:yidingx.zhou at intel.com> wrote:
> >
> > > The pcap file will be synchronized to the disk when stopping the device.
> > > It takes a long time if the file is large that would cause the
> > > 'detach sync request' timeout when the device is closed under
> > > multi-process scenario.
> > >
> > > This commit fixes the issue by using alarm handler to release dumper.
> > >
> > > Fixes: 0ecfb6c04d54 ("net/pcap: move handler to process private")
> > > Cc: mailto:stable at dpdk.org
> > >
> > > Signed-off-by: Yiding Zhou <mailto:yidingx.zhou at intel.com>
> >
> >
> > I think you need to redesign the handshake if this the case.
> > Forcing 30 second delay at the end of all uses of pcap is not acceptable.
> 
> @Zhang, Qi Z Do we need to redesign the handshake to fix this?

Hi, Ferruh
Sorry for the late reply.
I did not receive your email on Oct 6, I got your comments from patchwork.

"Can you please provide more details on multi-process communication and 
call trace, to help us think about a solution to address this issue in a 
more generic way (not just for pcap but for any case device close takes 
more than multi-process timeout)?"

I try to explain this issue with a sequence diagram, hope it can be displayed correctly in the mail.

       thread                                 intr thread           intr thread             thread
    of secondary                       of secondary          of primary          of primary
             |                                              |                         |                          |
             |                                              |                         |                          |
rte_eal_hotplug_remove
rte_dev_remove
eal_dev_hotplug_request_to_primary
rte_mp_request_sync ------------------------------------------------------->|
                                                                                                                    |
                                                                                              handle_secondary_request
                                                                                         |<-----------------|
                                                                                         |
                                                                   __handle_secondary_request
                                                          eal_dev_hotplug_request_to_secondary
           |<------------------------------------- rte_mp_request_sync
           |
handle_primary_request--------->|
                                                           |
                            __handle_primary_request
                               local_dev_remove(this will take long time)
                                            rte_mp_reply -------------------------------->|                              
                                                                                         |
                                                                             local_dev_remove
          |<------------------------------------------------- rte_mp_reply

The marked 'local_dev_remove()' in the secondary process will perform a pcap file synchronization operation.
When the pcap file is too large, it will take a lot of time (according to my test 100G takes 20+ seconds).
This caused the processing of hot_plug message to time out.