[Spice-devel] [PATCH spice-server 2/3] red-stream: Implements flush using TCP_CORK

[Frediano Ziglio]

> 
> On 04/13/2018 03:25 PM, Frediano Ziglio wrote:
> > Cork is a system interface implemented by Linux and some *BSD systems to
> > tell the system that other data are expected to be written to a socket.
> > This allows the system to reduce network fragmentation waiting for network
> > packets to be complete.
> > 
> > Using some replay capture and some instrumentation resulted in a
> > bandwith reduction of 11% and a packet reduction of 56%.
> > 
> > The tests was done using replay utility so results could be a bit different
> > from real cases as:
> > - replay goes as fast as it can, for instance packets could
> >    be merged by the kernel decreasing packet numbers and a bit
> >    byte spent (this actually make the following improves worse);
> > - there are fewer channels (no much cursor, sound, etc).
> > The following tests shows count packet and total bytes from server to
> > client using a real network. I used a direct cable connection using 1gb
> > connection and 2 laptops.
> > 
> > cork: 537 1582240
> > cork: 681 1823754
> > cork: 524 1583287
> > cork: 538 1582350
> > no cork: 1329 1834630
> > no cork: 1290 1829094
> > no cork: 1289 1830164
> > no cork: 1317 1833589
> > no cork: 1320 1835705
> > 
> > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > ---
> >   server/red-stream.c | 40 +++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 39 insertions(+), 1 deletion(-)
> > 
> > diff --git a/server/red-stream.c b/server/red-stream.c
> > index 9a9c1a0f..18c4a935 100644
> > --- a/server/red-stream.c
> > +++ b/server/red-stream.c
> > @@ -24,6 +24,7 @@
> >   #include <unistd.h>
> >   #include <sys/socket.h>
> >   #include <fcntl.h>
> > +#include <netinet/tcp.h>
> >   
> >   #include <glib.h>
> >   
> > @@ -37,6 +38,11 @@
> >   #include "red-stream.h"
> >   #include "reds.h"
> >   
> > +// compatibility for *BSD systems
> > +#ifndef TCP_CORK
> > +#define TCP_CORK TCP_NOPUSH
> > +#endif
> > +
> >   struct AsyncRead {
> >       void *opaque;
> >       uint8_t *now;
> > @@ -83,6 +89,8 @@ struct RedStreamPrivate {
> >        * deallocated when main_dispatcher handles the
> >        SPICE_CHANNEL_EVENT_DISCONNECTED
> >        * event, either from same thread or by call back from main thread.
> >        */
> >       SpiceChannelEventInfo* info;
> > +    bool use_cork;
> > +    bool corked;
> >   
> >       ssize_t (*read)(RedStream *s, void *buf, size_t nbyte);
> >       ssize_t (*write)(RedStream *s, const void *buf, size_t nbyte);
> > @@ -92,6 +100,16 @@ struct RedStreamPrivate {
> >       SpiceCoreInterfaceInternal *core;
> >   };
> >   
> > +/**
> > + * Set TCP_CORK on socket
> > + */
> > +/* NOTE: enabled must be int */
> > +static int socket_set_cork(int socket, int enabled)
> > +{
> > +    SPICE_VERIFY(sizeof(enabled) == sizeof(int));
> > +    return setsockopt(socket, IPPROTO_TCP, TCP_CORK, &enabled,
> > sizeof(enabled));
> > +}
> > +
> >   static ssize_t stream_write_cb(RedStream *s, const void *buf, size_t
> >   size)
> >   {
> >       return write(s->socket, buf, size);
> > @@ -205,11 +223,31 @@ bool red_stream_write_all(RedStream *stream, const
> > void *in_buf, size_t n)
> >   
> >   bool red_stream_set_auto_flush(RedStream *s, bool auto_flush)
> >   {
> > -    return auto_flush;
> > +    if (s->priv->use_cork == !auto_flush) {
> > +        return true;
> > +    }
> > +
> > +    s->priv->use_cork = !auto_flush;
> > +    if (s->priv->use_cork) {
> > +        if (socket_set_cork(s->socket, 1)) {
> > +            s->priv->use_cork = false;
> > +            return false;
> > +        } else {
> > +            s->priv->corked = true;
> > +        }
> > +    } else if (s->priv->corked) {
> > +        socket_set_cork(s->socket, 0);
> > +        s->priv->corked = false;
> > +    }
> Hi Frediano,
> 
> It would be simpler to use !auto_flash or s->priv->use_cork
> and also only keep one of use_cork and corked.
> Possibly the logic is a bit different and not exactly what you want.
> 
>        if (socket_set_cork(s->socket, !auto_flash)) {
>            return false;
>        }
> 
>        s->priv->use_cork = !auto_flash;
> 
> 
> > +    return true;
> >   }
> 
> Uri.
> 

Not proper... the exact equivalent is this:


bool red_stream_set_auto_flush_new(RedStream *s, bool auto_flush)
{
    if (s->priv->use_cork == !auto_flush) {
        return true;
    }

    if (!auto_flush || s->priv->corked) {
        if (socket_set_cork(s->socket, !auto_flush) && !auto_flush) {
            return false;
        }
        s->priv->corked = !auto_flush;
    }

    s->priv->use_cork = !auto_flush;
    return true;
}


but is confusing, maybe easier to remove the "} else {" after a return
and move use_cork change after the ifs as suggested to avoid assigning
to false, like:


--- a/server/red-stream.c
+++ b/server/red-stream.c
@@ -227,18 +227,16 @@ bool red_stream_set_auto_flush(RedStream *s, bool auto_flush)
         return true;
     }

-    s->priv->use_cork = !auto_flush;
-    if (s->priv->use_cork) {
+    if (!auto_flush) {
         if (socket_set_cork(s->socket, 1)) {
-            s->priv->use_cork = false;
             return false;
-        } else {
-            s->priv->corked = true;
         }
+        s->priv->corked = true;
     } else if (s->priv->corked) {
         socket_set_cork(s->socket, 0);
         s->priv->corked = false;
     }
+    s->priv->use_cork = !auto_flush;
     return true;
 }


A bit longer than the previous but IMO more readable.

> >   
> >   void red_stream_flush(RedStream *s)
> >   {
> > +    if (s->priv->corked) {
> > +        socket_set_cork(s->socket, 0);
> > +        socket_set_cork(s->socket, 1);
> > +    }
> >   }
> >   
> >   #if HAVE_SASL
> > 
> 
> 

Frediano