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

[Uri Lublin]

On 04/17/2018 08:50 PM, Frediano Ziglio wrote:
>>
>> 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:

I know it's not equivalent, but simpler.

Do we really need both use_cork and corked ?

Even if corked==FALSE , still socket_set_cork(s->socket, 0)
would succeed.

Uri.

> 
> 
> 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
>