linux-kernel - RE: [[PATCH v1] 25/37] [CIFS] SMBD: Support SMBD idle connection timer

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Message-ID: <CY4PR21MB01829585183A42669B962B4AA08C0@CY4PR21MB0182.namprd21.prod.outlook.com>
Date:   Mon, 14 Aug 2017 23:42:13 +0000
From:   Tom Talpey <ttalpey@...rosoft.com>
To:     Long Li <longli@...rosoft.com>, Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [[PATCH v1] 25/37] [CIFS] SMBD: Support SMBD idle connection
 timer

> -----Original Message-----
> From: linux-cifs-owner@...r.kernel.org [mailto:linux-cifs-
> owner@...r.kernel.org] On Behalf Of Long Li
> Sent: Monday, August 14, 2017 7:30 PM
> To: Tom Talpey <ttalpey@...rosoft.com>; Steve French <sfrench@...ba.org>;
> linux-cifs@...r.kernel.org; samba-technical@...ts.samba.org; linux-
> kernel@...r.kernel.org
> Subject: RE: [[PATCH v1] 25/37] [CIFS] SMBD: Support SMBD idle connection
> timer
> 
> [This sender failed our fraud detection checks and may not be who they appear
> to be. Learn about spoofing at http://aka.ms/LearnAboutSpoofing]
> 
> > -----Original Message-----
> > From: Tom Talpey
> > Sent: Monday, August 14, 2017 2:12 PM
> > To: Long Li <longli@...rosoft.com>; Steve French <sfrench@...ba.org>;
> > linux-cifs@...r.kernel.org; samba-technical@...ts.samba.org; linux-
> > kernel@...r.kernel.org
> > Cc: Long Li <longli@...rosoft.com>
> > Subject: RE: [[PATCH v1] 25/37] [CIFS] SMBD: Support SMBD idle connection
> > timer
> >
> > > -----Original Message-----
> > > From: linux-cifs-owner@...r.kernel.org [mailto:linux-cifs-
> > > owner@...r.kernel.org] On Behalf Of Long Li
> > > Sent: Wednesday, August 2, 2017 4:11 PM
> > > To: Steve French <sfrench@...ba.org>; linux-cifs@...r.kernel.org;
> > > samba- technical@...ts.samba.org; linux-kernel@...r.kernel.org
> > > Cc: Long Li <longli@...rosoft.com>
> > > Subject: [[PATCH v1] 25/37] [CIFS] SMBD: Support SMBD idle connection
> > > timer
> > >
> > > +static int keep_alive_interval = 120;
> >
> > This is the recommended value, but not the only possibility.
> >
> > > @@ -1348,6 +1369,10 @@ struct cifs_rdma_info*
> > cifs_create_rdma_session(
> > >         init_waitqueue_head(&info->wait_send_queue);
> > >         init_waitqueue_head(&info->wait_reassembly_queue);
> > >
> > > +       INIT_DELAYED_WORK(&info->idle_timer_work,
> > idle_connection_timer);
> > > +       schedule_delayed_work(&info->idle_timer_work,
> > > +               info->keep_alive_interval*HZ);
> > > +
> >
> > This initialization is ok, but the timer should be rescheduled (extended) any
> > time any packet is sent. There is no need to perform keepalives on an active
> > SMB Direct connection.
> 
> My feeling is that rescheduling on a work queue for every packet is sent is not
> efficient, especially under heavy conditions.

That's not what I was suggesting. Cant the timer simply be re-extended to the
120-second interval? I.e. on an active connection, it will never fire because it's
always advancing.

As defined here, it will go off and send a keepalive every 120 seconds. The
idle_connection_timer() routine unconditionally sends it.

> 
> Firing it every 120 seconds doesn't seem to be big waste and may actually save
> some CPU.

Firing the timer, no big deal. Sending the packets and requiring the peer to process
them too, disagree.

Tom.