RFsim: don't shell out to improve kernel socket buffer sizes, teach the user instead

A later commit in this series adds performance tuning tips, which
includes the call made in RFsim until this commit.

radio/rfsimulator/README.md

@@ -174,3 +174,18 @@ To successfully establish a connection with such a GEO satellite channel, both g
 # Caveats
 
 There are issues in power control: txgain/rxgain setting is not supported.
+
+# How to improve performance
+
+Most importantly, note that the RFsimulator is not designed to be as performant
+as possible, nor is it designed to run close to real-time. It might run faster
+or slower than realtime, depending on CPU, and by design, as this allows to
+stop the entire system for inspection, e.g., using a debugger.
+
+In order to improve performance, you can modify the radio parameters of the gNB
+to reduce the amount of transported samples:
+
+- Use option `-E` for three-quarter sampling (also to be done on the UE-side!)
+- Prefer smaller cell bandwidths
+
+A possible, unimplemented optimization would be to compress samples.

radio/rfsimulator/simulator.c

@@ -86,8 +86,7 @@
 //
 // #define MAX_FD_RFSIMU FD_SETSIZE
 #define MAX_FD_RFSIMU 250
-#define SYSCTL_MEM_VALUE 134217728 // Kernel network buffer size
+#define SEND_BUFF_SIZE 100000000 // Socket buffer size
-#define SEND_BUFF_SIZE SYSCTL_MEM_VALUE // Socket buffer size
 
 // Simulator role
 typedef enum { SIMU_ROLE_SERVER = 1, SIMU_ROLE_CLIENT } simuRole;
@@ -540,40 +539,6 @@ static int rfsimu_vtime_cmd(char *buff, int debug, telnet_printfunc_t prnt, void
   return CMDSTATUS_FOUND;
 }
 
-static void customNetForPerf()
-{
-  int res = 0;
-  char sysctlmem[256];
-  memset(sysctlmem, 0, 256);
-  sprintf(sysctlmem, "/sbin/sysctl -n -e -q -w net.core.rmem_default=%d", SYSCTL_MEM_VALUE);
-  LOG_W(HW, "running command \"%s\" to increase RFsim performance\n", sysctlmem);
-  res = system(sysctlmem);
-  if (res != 0) {
-    LOG_W(HW, "Cannot set net.core.rmem_default to %d\n", SYSCTL_MEM_VALUE);
-  }
-  memset(sysctlmem, 0, 256);
-  sprintf(sysctlmem, "/sbin/sysctl -n -e -q -w net.core.rmem_max=%d", SYSCTL_MEM_VALUE);
-  LOG_W(HW, "running command \"%s\" to increase RFsim performance\n", sysctlmem);
-  res = system(sysctlmem);
-  if (res != 0) {
-    LOG_W(HW, "Cannot set net.core.rmem_max to %d\n", SYSCTL_MEM_VALUE);
-  }
-  memset(sysctlmem, 0, 256);
-  sprintf(sysctlmem, "/sbin/sysctl -n -e -q -w net.core.wmem_default=%d", SYSCTL_MEM_VALUE);
-  LOG_W(HW, "running command \"%s\" to increase RFsim performance\n", sysctlmem);
-  res = system(sysctlmem);
-  if (res != 0) {
-    LOG_W(HW, "Cannot set net.core.wmem_default to %d\n", SYSCTL_MEM_VALUE);
-  }
-  memset(sysctlmem, 0, 256);
-  sprintf(sysctlmem, "/sbin/sysctl -n -e -q -w net.core.wmem_max=%d", SYSCTL_MEM_VALUE);
-  LOG_W(HW, "running command \"%s\" to increase RFsim performance\n", sysctlmem);
-  res = system(sysctlmem);
-  if (res != 0) {
-    LOG_W(HW, "Cannot set net.core.wmem_max to %d\n", SYSCTL_MEM_VALUE);
-  }
-}
-
 static int startServer(openair0_device *device) {
   rfsimulator_state_t *t = (rfsimulator_state_t *) device->priv;
   t->role = SIMU_ROLE_SERVER;
@@ -588,7 +553,6 @@ static int startServer(openair0_device *device) {
     return -1;
   }
   struct sockaddr_in addr = {.sin_family = AF_INET, .sin_port = htons(t->port), .sin_addr = {.s_addr = INADDR_ANY}};
-  customNetForPerf();
   int rc = bind(t->listen_sock, (struct sockaddr *)&addr, sizeof(addr));
   if (rc < 0) {
     LOG_E(HW, "bind() failed, errno(%d)\n", errno);
@@ -620,7 +584,6 @@ static int startClient(openair0_device *device) {
   addr.sin_addr.s_addr = inet_addr(t->ip);
   bool connected=false;
 
-  customNetForPerf();
   while(!connected) {
     LOG_I(HW, "Trying to connect to %s:%d\n", t->ip, t->port);