issue: 4260620 infinite loop latency spec

When there are no offloaded sockets, we mistakingly poll for
offloaded sockets in case VMA_SELECT_POLL_OS_FORCE=1.

This behavior makes us getting stuck in an infinite loop.

This patch fixes the issue by polling OS sockets
in the case there are no offloaded sockets
regardless to VMA_SELECT_POLL_OS_FORCE value.

Signed-off-by: Tomer Cabouly <[email protected]>

README

@@ -627,8 +627,8 @@ Where value of 0 is used for no polling (interrupt driven)
 Default value is 100000
 
 VMA_SELECT_POLL_OS_FORCE
-This flag forces to poll the OS file descriptors while user thread calls
-select(), poll() or epoll_wait() even when no offloaded sockets are mapped.
+NOTE: 
+This is a DEPRECATED configuration parameter that will be removed from future libvma releases.
 Enabling this flag causes VMA to set VMA_SELECT_POLL_OS_RATIO and
 VMA_SELECT_SKIP_OS to 1. This will result in VMA_SELECT_POLL number of
 times VMA will poll the OS file descriptors, along side with offloaded

src/vma/iomux/io_mux_call.cpp

@@ -171,7 +171,6 @@ io_mux_call::io_mux_call(int *off_fds_buffer, offloaded_mode_t *off_modes_buffer
 	m_n_sysvar_select_skip_os_fd_check(safe_mce_sys().select_skip_os_fd_check),
 	m_n_sysvar_select_poll_os_ratio(safe_mce_sys().select_poll_os_ratio),
 	m_n_sysvar_select_poll_num(safe_mce_sys().select_poll_num),
-	m_b_sysvar_select_poll_os_force(safe_mce_sys().select_poll_os_force),
 	m_b_sysvar_select_handle_cpu_usage_stats(safe_mce_sys().select_handle_cpu_usage_stats),
 	m_p_all_offloaded_fds(off_fds_buffer),
 	m_p_offloaded_modes(off_modes_buffer),
@@ -469,8 +468,7 @@ int io_mux_call::call()
 
 	__log_funcall("");
 
-	if (!m_b_sysvar_select_poll_os_force  // TODO: evaluate/consider this logic
-			&& (*m_p_num_all_offloaded_fds == 0))
+	if (*m_p_num_all_offloaded_fds == 0)
 	{
 		// 1st scenario
 		timer_update();

src/vma/iomux/io_mux_call.h

@@ -240,7 +240,6 @@ class io_mux_call
 	const uint32_t m_n_sysvar_select_skip_os_fd_check;
 	const uint32_t m_n_sysvar_select_poll_os_ratio;
 	const int32_t m_n_sysvar_select_poll_num;
-	const bool m_b_sysvar_select_poll_os_force;
 	const bool m_b_sysvar_select_handle_cpu_usage_stats;
 
 public:

src/vma/main.cpp

@@ -481,7 +481,6 @@ void print_vma_global_settings()
 	VLOG_PARAM_STRING("Force Flowtag for MC", safe_mce_sys().mc_force_flowtag, MCE_DEFAULT_MC_FORCE_FLOWTAG, SYS_VAR_MC_FORCE_FLOWTAG, safe_mce_sys().mc_force_flowtag ? "Enabled " : "Disabled");
 
 	VLOG_PARAM_NUMBER("Select Poll (usec)", safe_mce_sys().select_poll_num, MCE_DEFAULT_SELECT_NUM_POLLS, SYS_VAR_SELECT_NUM_POLLS);
-	VLOG_PARAM_STRING("Select Poll OS Force", safe_mce_sys().select_poll_os_force, MCE_DEFAULT_SELECT_POLL_OS_FORCE, SYS_VAR_SELECT_POLL_OS_FORCE, safe_mce_sys().select_poll_os_force ? "Enabled " : "Disabled");
 
 	if (safe_mce_sys().select_poll_os_ratio) {
 		VLOG_PARAM_NUMBER("Select Poll OS Ratio", safe_mce_sys().select_poll_os_ratio, MCE_DEFAULT_SELECT_POLL_OS_RATIO, SYS_VAR_SELECT_POLL_OS_RATIO);

src/vma/util/sys_vars.cpp

@@ -703,8 +703,8 @@ void mce_sys_var::get_env_params()
 		mem_alloc_type 		= ALLOC_TYPE_HUGEPAGES; //MCE_DEFAULT_MEM_ALLOC_TYPE (ALLOC_TYPE_CONTIG)
 		strcpy(internal_thread_affinity_str, "0"); //MCE_DEFAULT_INTERNAL_THREAD_AFFINITY_STR ("-1")
 		progress_engine_interval_msec = 100; //MCE_DEFAULT_PROGRESS_ENGINE_INTERVAL_MSEC (10)
-		select_poll_os_ratio          = 100; //MCE_DEFAULT_SELECT_POLL_OS_RATIO (10)
-		select_poll_os_force	      = 1;   //MCE_DEFAULT_SELECT_POLL_OS_FORCE (0)
+		select_poll_os_ratio          = 1; //MCE_DEFAULT_SELECT_POLL_OS_RATIO (10)
+		select_skip_os_fd_check	      = 1;   //MCE_DEFAULT_SELECT_SKIP_OS (4)
 		tcp_nodelay	      	      = true; // MCE_DEFAULT_TCP_NODELAY (falst)
 		ring_dev_mem_tx          = 16384; // MCE_DEFAULT_RING_DEV_MEM_TX (0)
 		break;