[Spice-devel] [PATCH] Use non-zero data for initial ping

[Yaniv Kaul]

While the best thing would have been to pass the first image already to 
the client using those 256K (and calculate the bandwidth based on the 
first data passed to the client and continue to do so, as the protocol 
continues), the next best thing would probably be pass *some* image to 
the client - some JPEG compressed logo or something.
This is:
(1) already quite compressed.
(2) useful in some way.
(3) probably 'cheaper' than creating some random data.

I think QEMU has this feature (off by default) to load a bootsplash 
image as part of the BIOS. I wonder if it can be somehow re-used.

Y.


On 02/13/2012 09:48 PM, Dan McGee wrote:
> This prevents compression over things such as VPN links misleading us on
> available bandwidth. The page used before was 4K worth of zeroes, which
> isn't a very realistic test at all.
>
> We now use a generated sequence of bytes that vary in value and offset
> between consecutive values, causing compression programs to have a much
> harder time reducing our ping packets to nothing.
>
> Here are some comparisons of before/after using a small standalone
> program that generates bytes in the same fashion:
>
> Before:
>      4096 zerodata
>      43   zerodata.bz2
>      38   zerodata.gz
>      92   zerodata.xz
>
> After:
>      4096 seqdata
>      1213 seqdata.bz2
>      4119 seqdata.gz
>      3208 seqdata.xz
>
> Signed-off-by: Dan McGee<dpmcgee at gmail.com>
> ---
>
> This was a TODO item on the following page:
> http://spice-space.org/page/Features/Bandwidth_monitoring
>
> The standalone test program is below if anyone wants to try it out; simply pass
> '4096' or similar as the first argument and you will get 4096 "random" bytes on
> stdout that you can play with.
>
> #include<stdio.h>
> #include<stdlib.h>
>
> int main(int argc, char *argv[])
> {
> 	int i, total;
>
> 	total = atoi(argv[1]);
>
> 	for(i = 0; i<  total; i++) {
> 		div_t result = div(i, 256);
> 		if(result.quot % 2 == 0) {
> 			fputc((result.quot + 1) * result.rem, stdout);
> 		} else {
> 			fputc(512 - (result.quot * result.rem), stdout);
> 		}
> 	}
> 	return 0;
> }
>
>
>   server/main_channel.c |   24 ++++++++++++++++--------
>   1 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/server/main_channel.c b/server/main_channel.c
> index f7e1ab0..2ce20c0 100644
> --- a/server/main_channel.c
> +++ b/server/main_channel.c
> @@ -22,6 +22,7 @@
>   #include<inttypes.h>
>   #include<stdint.h>
>   #include<stdio.h>
> +#include<stdlib.h>
>   #include<unistd.h>
>   #include<sys/socket.h>
>   #include<netinet/in.h>
> @@ -45,8 +46,6 @@
>   #include "red_channel.h"
>   #include "generated_marshallers.h"
>
> -#define ZERO_BUF_SIZE 4096
> -
>   #define REDS_MAX_SEND_IOVEC 100
>
>   #define NET_TEST_WARMUP_BYTES 0
> @@ -54,8 +53,6 @@
>
>   #define PING_INTERVAL (1000 * 10)
>
> -static uint8_t zero_page[ZERO_BUF_SIZE] = {0};
> -
>   typedef struct RedsOutItem RedsOutItem;
>   struct RedsOutItem {
>       PipeItem base;
> @@ -335,17 +332,28 @@ static void main_channel_marshall_ping(SpiceMarshaller *m, int size, int ping_id
>   {
>       struct timespec time_space;
>       SpiceMsgPing ping;
> +    uint8_t *ping_data;
> +    int i;
>
>       ping.id = ping_id;
>       clock_gettime(CLOCK_MONOTONIC,&time_space);
>       ping.timestamp = time_space.tv_sec * 1000000LL + time_space.tv_nsec / 1000LL;
>       spice_marshall_msg_ping(m,&ping);
>
> -    while (size>  0) {
> -        int now = MIN(ZERO_BUF_SIZE, size);
> -        size -= now;
> -        spice_marshaller_add_ref(m, zero_page, now);
> +    ping_data = spice_malloc(size);
> +    /* this produces ascending and descending byte runs which vary in offset
> +     * every 512 bytes, preventing prevents compression from being able to
> +     * influence the resulting size of the ping data too much */
> +    for(i = 0; i<  size; i++) {
> +        div_t result = div(i, 256);
> +        if(result.quot % 2 == 0) {
> +            ping_data[i] = (result.quot + 1) * result.rem;
> +        } else {
> +            ping_data[i] = 512 - (result.quot * result.rem);
> +        }
>       }
> +
> +    spice_marshaller_add(m, ping_data, size);
>   }
>
>   void main_channel_push_mouse_mode(MainChannel *main_chan, int current_mode,