Re: [PATCH v3 2/2] net/colo-compare.c: handling of the full primary or secondary queue

[Derek Su]

Lukas Straub <address@hidden> 於 2020年3月28日 週六 上午1:46寫道：
>
> On Wed, 25 Mar 2020 17:43:54 +0800
> Derek Su <address@hidden> wrote:
>
> > The pervious handling of the full primary or queue is only dropping
> > the packet. If there are lots of clients to the guest VM,
> > the "drop" will lead to the lost of the networking connection
> > until next checkpoint.
> >
> > To address the issue, this patch drops the packet firstly.
> > Then, send all queued primary packets, remove all queued secondary
> > packets and do checkpoint.
> >
> > Signed-off-by: Derek Su <address@hidden>
> > ---
> >  net/colo-compare.c | 41 ++++++++++++++++++++++++++++++-----------
> >  1 file changed, 30 insertions(+), 11 deletions(-)
> >
> > diff --git a/net/colo-compare.c b/net/colo-compare.c
> > index cdd87b2aa8..1a52f50fbe 100644
> > --- a/net/colo-compare.c
> > +++ b/net/colo-compare.c
> > @@ -125,6 +125,12 @@ static const char *colo_mode[] = {
> >      [SECONDARY_IN] = "secondary",
> >  };
> >
> > +enum {
> > +    QUEUE_INSERT_ERR = -1,
> > +    QUEUE_INSERT_OK = 0,
> > +    QUEUE_INSERT_FULL = 1,
> > +};
> > +
> >  static int compare_chr_send(CompareState *s,
> >                              const uint8_t *buf,
> >                              uint32_t size,
> > @@ -211,8 +217,10 @@ static int colo_insert_packet(GQueue *queue, Packet 
> > *pkt, uint32_t *max_ack)
> >  }
> >
> >  /*
> > - * Return 0 on success, if return -1 means the pkt
> > - * is unsupported(arp and ipv6) and will be sent later
> > + * Return QUEUE_INSERT_OK on success.
> > + * If return QUEUE_INSERT_FULL means list is full, and
> > + * QUEUE_INSERT_ERR means the pkt is unsupported(arp and ipv6) and
> > + * will be sent later
> >   */
> >  static int packet_enqueue(CompareState *s, int mode, Connection **con)
> >  {
> > @@ -234,7 +242,7 @@ static int packet_enqueue(CompareState *s, int mode, 
> > Connection **con)
> >      if (parse_packet_early(pkt)) {
> >          packet_destroy(pkt, NULL);
> >          pkt = NULL;
> > -        return -1;
> > +        return QUEUE_INSERT_ERR;
> >      }
> >      fill_connection_key(pkt, &key);
> >
> > @@ -258,11 +266,12 @@ static int packet_enqueue(CompareState *s, int mode, 
> > Connection **con)
> >                       "drop packet", colo_mode[mode]);
> >          packet_destroy(pkt, NULL);
> >          pkt = NULL;
> > +        return QUEUE_INSERT_FULL;
> >      }
> >
> >      *con = conn;
> >
> > -    return 0;
> > +    return QUEUE_INSERT_OK;
> >  }
> >
> >  static inline bool after(uint32_t seq1, uint32_t seq2)
> > @@ -995,17 +1004,22 @@ static void compare_pri_rs_finalize(SocketReadState 
> > *pri_rs)
> >  {
> >      CompareState *s = container_of(pri_rs, CompareState, pri_rs);
> >      Connection *conn = NULL;
> > +    int ret;
> >
> > -    if (packet_enqueue(s, PRIMARY_IN, &conn)) {
> > +    ret = packet_enqueue(s, PRIMARY_IN, &conn);
> > +    if (ret == QUEUE_INSERT_OK) {
> > +        /* compare packet in the specified connection */
> > +        colo_compare_connection(conn, s);
> > +    } else if (ret == QUEUE_INSERT_FULL) {
> > +        g_queue_foreach(&s->conn_list, colo_flush_packets, s);
> > +        colo_compare_inconsistency_notify(s);
> > +    } else {
> >          trace_colo_compare_main("primary: unsupported packet in");
> >          compare_chr_send(s,
> >                           pri_rs->buf,
> >                           pri_rs->packet_len,
> >                           pri_rs->vnet_hdr_len,
> >                           false);
> > -    } else {
> > -        /* compare packet in the specified connection */
> > -        colo_compare_connection(conn, s);
> >      }
> >  }
> >
> > @@ -1013,12 +1027,17 @@ static void compare_sec_rs_finalize(SocketReadState 
> > *sec_rs)
> >  {
> >      CompareState *s = container_of(sec_rs, CompareState, sec_rs);
> >      Connection *conn = NULL;
> > +    int ret;
> >
> > -    if (packet_enqueue(s, SECONDARY_IN, &conn)) {
> > -        trace_colo_compare_main("secondary: unsupported packet in");
> > -    } else {
> > +    ret = packet_enqueue(s, SECONDARY_IN, &conn);
> > +    if (ret == QUEUE_INSERT_OK) {
> >          /* compare packet in the specified connection */
> >          colo_compare_connection(conn, s);
> > +    } else if (ret == QUEUE_INSERT_FULL) {
> > +        g_queue_foreach(&s->conn_list, colo_flush_packets, s);
> > +        colo_compare_inconsistency_notify(s);
> > +    } else {
> > +        trace_colo_compare_main("secondary: unsupported packet in");
> >      }
> >  }
> >
>
> Hi,
> I don't think we have to flush here because the (post-)checkpoint event will 
> flush the packets for us.
>

Hi,
Yes, the periodical checkpoint can flush the packets.

But, if many clients send many packets to the vm,
there is a high probability that packets are dropped because the
primary/secondary queues are always full.
It causes lots of re-transmission between clients and vm and
deteriorate service response to clients.

Sincerely,
Derek Su

> Regards,
> Lukas Straub