On Wed, 2012-03-14 at 20:49 -0500, Mike Christie wrote:
> On 03/14/2012 06:50 PM, Eddie Wai wrote:
> > During heavy I/O transmission, it was observed that network packets
> > can get dropped when no link flow control is enabled. When this happens,
> > I/O completions can exceed the default NOP transmission of 5s while the
> > hw send queue resource backs up. When the queue gets full, NOP
> > transmission requests will also get blocked. It was observed that
> > the NOP transmission requests will keep repeatedly try to send out
> > the NOP while holding the session lock. This is very intrusive as the
> > requests are being called on every timer execution since the last_ping
> > parameter doesn't get updated upon transmission failure. This creates a
> > tremendous bottleneck especially when the connection is about to get torn
> > down.
> >
> > This patch alleviates the pounding of the NOP transmission in the
> > iscsi_check_transport_timeouts routine by injecting an artifical 1s delay
> > in between each NOP transmission requests due to failures upon timeout.
> >
> > There is no need to keep pounding on to request this data provoking NOP
> > transmission continuously when the transmit queue is full.
> >
> > Please review and comment. Thanks.
> >
> >
> > Signed-off-by: Eddie Wai <eddie....@broadcom.com>
> > ---
> > drivers/scsi/libiscsi.c | 13 +++++++++----
> > 1 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> > index 82c3fd4..f1141a8 100644
> > --- a/drivers/scsi/libiscsi.c
> > +++ b/drivers/scsi/libiscsi.c
> > @@ -940,13 +940,14 @@ static void iscsi_tmf_rsp(struct iscsi_conn *conn,
> > struct iscsi_hdr *hdr)
> > wake_up(&conn->ehwait);
> > }
> >
> > -static void iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin
> > *rhdr)
> > +static struct iscsi_task *iscsi_send_nopout(struct iscsi_conn *conn,
> > + struct iscsi_nopin *rhdr)
> > {
> > struct iscsi_nopout hdr;
> > struct iscsi_task *task;
> >
> > if (!rhdr && conn->ping_task)
> > - return;
> > + return NULL;
> >
> > memset(&hdr, 0, sizeof(struct iscsi_nopout));
> > hdr.opcode = ISCSI_OP_NOOP_OUT | ISCSI_OP_IMMEDIATE;
> > @@ -967,6 +968,7 @@ static void iscsi_send_nopout(struct iscsi_conn *conn,
> > struct iscsi_nopin *rhdr)
> > conn->ping_task = task;
> > conn->last_ping = jiffies;
> > }
> > + return task;
> > }
> >
> > static int iscsi_nop_out_rsp(struct iscsi_task *task,
> > @@ -2059,8 +2061,11 @@ static void iscsi_check_transport_timeouts(unsigned
> > long data)
> > if (time_before_eq(last_recv + recv_timeout, jiffies)) {
> > /* send a ping to try to provoke some traffic */
> > ISCSI_DBG_CONN(conn, "Sending nopout as ping\n");
> > - iscsi_send_nopout(conn, NULL);
> > - next_timeout = conn->last_ping + (conn->ping_timeout * HZ);
> > + if (iscsi_send_nopout(conn, NULL))
> > + next_timeout = conn->last_ping +
> > + (conn->ping_timeout * HZ);
>
> Once we send a ping, we should not run this timer again until it has
> timed out Why is the ping not timing out and then why are not hitting
> the check above this that just returns?
The problem is that it is the right time to send the ping but the
request was not successful due to a lack of task resources. The
send_pdu will then returned a NULL task which prevented the
conn->last_ping parameter from being updated. So when this timer
routine exits, it comes right back with the last_recv and last_ping both
being the old value since there wasn't any new completions either.
>
> Is the timer firing early, so we keep hitting the iscsi_send_nopout path?
>
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