From 89342618773b64db3e67701c0cd9dd89cdbbc18a Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Thu, 27 Oct 2016 16:05:06 +0100 Subject: [PATCH] Get pending events in random Nowadays, we select events to be reported to GDB in random, however that is not enough when many GDBserver internal events (not reported to GDB) are generated. GDBserver pulls all events out of kernel via waitpid, and leave them pending. When goes through threads which have pending events, GDBserver uses find_inferior to find the first thread which has pending event, and consumes it. Note that find_inferior always iterate threads in a fixed order. If multiple threads keep hitting GDBserver breakpoints, range stepping with single-step breakpoint for example, threads in the head of the thread list are more likely to be processed and threads in the tail are starved. This causes some timeout fails in gdb.threads/non-stop-fair-events.exp when range stepping is enabled on arm-linux. This patch fixes this issue by randomly selecting pending events. It adds a new function find_inferior_in_random, which iterates threads which have pending events randomly. gdb/gdbserver: 2016-10-27 Yao Qi * inferiors.c (find_inferior_in_random): New function. * inferiors.h (find_inferior_in_random): Declare. * linux-low.c (linux_wait_for_event_filtered): Call find_inferior_in_random instead of find_inferior. --- gdb/gdbserver/ChangeLog | 7 ++++++ gdb/gdbserver/inferiors.c | 45 +++++++++++++++++++++++++++++++++++++++ gdb/gdbserver/inferiors.h | 5 +++++ gdb/gdbserver/linux-low.c | 6 ++++-- 4 files changed, 61 insertions(+), 2 deletions(-) diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index d43a96a0aee..c6bc016ce81 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,10 @@ +2016-10-27 Yao Qi + + * inferiors.c (find_inferior_in_random): New function. + * inferiors.h (find_inferior_in_random): Declare. + * linux-low.c (linux_wait_for_event_filtered): Call + find_inferior_in_random instead of find_inferior. + 2016-10-27 Yao Qi * linux-low.c (linux_wait_1): If single-step breakpoints are diff --git a/gdb/gdbserver/inferiors.c b/gdb/gdbserver/inferiors.c index 7888f3c1852..574a7ba7d57 100644 --- a/gdb/gdbserver/inferiors.c +++ b/gdb/gdbserver/inferiors.c @@ -248,6 +248,51 @@ find_inferior (struct inferior_list *list, return NULL; } +/* Find the random inferior_list_entry E in LIST for which FUNC (E, ARG) + returns non-zero. If no entry is found then return NULL. */ + +struct inferior_list_entry * +find_inferior_in_random (struct inferior_list *list, + int (*func) (struct inferior_list_entry *, void *), + void *arg) +{ + struct inferior_list_entry *inf = list->head; + int count = 0; + int random_selector; + + /* First count how many interesting entries we have. */ + while (inf != NULL) + { + struct inferior_list_entry *next; + + next = inf->next; + if ((*func) (inf, arg)) + count++; + inf = next; + } + + if (count == 0) + return NULL; + + /* Now randomly pick an entry out of those. */ + random_selector = (int) + ((count * (double) rand ()) / (RAND_MAX + 1.0)); + + inf = list->head; + while (inf != NULL) + { + struct inferior_list_entry *next; + + next = inf->next; + if ((*func) (inf, arg) && (random_selector-- == 0)) + return inf; + inf = next; + } + + gdb_assert_not_reached ("failed to find an inferior in random."); + return NULL; +} + struct inferior_list_entry * find_inferior_id (struct inferior_list *list, ptid_t id) { diff --git a/gdb/gdbserver/inferiors.h b/gdb/gdbserver/inferiors.h index 65ab1c6fc60..6ea7a999d59 100644 --- a/gdb/gdbserver/inferiors.h +++ b/gdb/gdbserver/inferiors.h @@ -154,6 +154,11 @@ struct inferior_list_entry *find_inferior void *arg); struct inferior_list_entry *find_inferior_id (struct inferior_list *list, ptid_t id); +struct inferior_list_entry * + find_inferior_in_random (struct inferior_list *, + int (*func) (struct inferior_list_entry *, + void *), + void *arg); void *inferior_target_data (struct thread_info *); void set_inferior_target_data (struct thread_info *, void *); diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index a463774971b..5dcf376ecf6 100644 --- a/gdb/gdbserver/linux-low.c +++ b/gdb/gdbserver/linux-low.c @@ -2700,7 +2700,8 @@ linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid, if (ptid_equal (filter_ptid, minus_one_ptid) || ptid_is_pid (filter_ptid)) { event_thread = (struct thread_info *) - find_inferior (&all_threads, status_pending_p_callback, &filter_ptid); + find_inferior_in_random (&all_threads, status_pending_p_callback, + &filter_ptid); if (event_thread != NULL) event_child = get_thread_lwp (event_thread); if (debug_threads && event_thread) @@ -2811,7 +2812,8 @@ linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid, /* ... and find an LWP with a status to report to the core, if any. */ event_thread = (struct thread_info *) - find_inferior (&all_threads, status_pending_p_callback, &filter_ptid); + find_inferior_in_random (&all_threads, status_pending_p_callback, + &filter_ptid); if (event_thread != NULL) { event_child = get_thread_lwp (event_thread); -- 2.30.2