* Alexey Perevalov (a.pereva...@samsung.com) wrote:
> It could help to track down vCPU state during page fault and
> page fault sources.
>
> This patch showes proc's status/stack/syscall file at the moment of pagefault,
> it's very interesting to know who was page fault initiator.
This is a LOT of debug code, almost none of it is postcopy specific,
so probably a question for generic tracing code; but I'll admit to
not being happy about the idea of putting this much code in for
this type of dumping; when it gets this desperate we just normally do
a special build.
However, some specific comments as well.
> Signed-off-by: Alexey Perevalov <a.pereva...@samsung.com>
> ---
> migration/postcopy-ram.c | 98
> +++++++++++++++++++++++++++++++++++++++++++++++-
> migration/trace-events | 6 +++
> 2 files changed, 103 insertions(+), 1 deletion(-)
>
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 42330fd..513633c 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -412,7 +412,91 @@ static int ram_block_enable_notify(const char
> *block_name, void *host_addr,
> return 0;
> }
>
> -static int get_mem_fault_cpu_index(uint32_t pid)
> +#define PROC_LEN 1024
> +#define DEBUG_FAULT_PROCESS_STATUS 1
> +
> +#ifdef DEBUG_FAULT_PROCESS_STATUS
> +
> +static FILE *get_proc_file(const gchar *frmt, pid_t thread_id)
> +{
> + FILE *f = NULL;
> + gchar *file_path = g_strdup_printf(frmt, thread_id);
> + if (file_path == NULL) {
> + error_report("Couldn't allocate path for %u", thread_id);
> + return NULL;
> + }
I was going to say that I thought g_strdup_printf couldn't
return NULL; but then I looked at the source - eww it can.
> + f = fopen(file_path, "r");
> + if (!f) {
> + error_report("can't open %s", file_path);
> + }
> +
> + trace_get_proc_file(file_path);
> + g_free(file_path);
> + return f;
> +}
> +
> +typedef void(*proc_line_handler)(const char *line);
> +
> +static void proc_line_cb(const char *line)
> +{
> + /* trace_ functions are inline */
> + trace_proc_line_cb(line);
> +}
> +
> +static void foreach_line_in_file(FILE *f, proc_line_handler cb)
> +{
> + char *line = NULL;
> + ssize_t read;
> + size_t len;
> +
> + while ((read = getline(&line, &len, f)) != -1) {
> + /* workaround, trace_ infrastructure already insert \n
> + * and getline includes it */
> + ssize_t str_len = strlen(line) - 1;
> + if (str_len <= 0)
> + continue;
> + line[str_len] = '\0';
> + cb(line);
> + }
> + free(line);
> +}
> +
> +static void observe_thread_proc(const gchar *path_frmt, pid_t thread_id)
> +{
> + FILE *f = get_proc_file(path_frmt, thread_id);
> + if (!f) {
> + error_report("can't read thread's proc");
> + return;
> + }
> +
> + foreach_line_in_file(f, proc_line_cb);
> + fclose(f);
> +}
> +
> +/*
> + * for convinience tracing need to trace
> + * observe_thread_begin
> + * get_proc_file
> + * proc_line_cb
> + * observe_thread_end
> + */
> +static void observe_thread(const char *msg, pid_t thread_id)
> +{
> + trace_observe_thread_begin(msg);
> + observe_thread_proc("/proc/%d/status", thread_id);
> + observe_thread_proc("/proc/%d/syscall", thread_id);
> + observe_thread_proc("/proc/%d/stack", thread_id);
You could wrap that in something like:
if (TRACE_PROC_LINE_CB_ENABLED) {
so it doesn't read all of the files and do all the allocation
to get to the point it realised no one cared.
Dave
> + trace_observe_thread_end(msg);
> +}
> +
> +#else
> +static void observe_thread(const char *msg, pid_t thread_id)
> +{
> +}
> +
> +#endif /* DEBUG_FAULT_PROCESS_STATUS */
> +
> +static int get_mem_fault_cpu_index(pid_t pid)
> {
> CPUState *cpu_iter;
>
> @@ -421,9 +505,20 @@ static int get_mem_fault_cpu_index(uint32_t pid)
> return cpu_iter->cpu_index;
> }
> trace_get_mem_fault_cpu_index(pid);
> + observe_thread("not a vCPU", pid);
> +
> return -1;
> }
>
> +static void observe_vcpu_state(void)
> +{
> + CPUState *cpu_iter;
> + CPU_FOREACH(cpu_iter) {
> + observe_thread("vCPU", cpu_iter->thread_id);
> + trace_vcpu_state(cpu_iter->running, cpu_iter->cpu_index);
> + }
> +}
> +
> /*
> * Handle faults detected by the USERFAULT markings
> */
> @@ -465,6 +560,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
> }
>
> ret = read(mis->userfault_fd, &msg, sizeof(msg));
> + observe_vcpu_state();
> if (ret != sizeof(msg)) {
> if (errno == EAGAIN) {
> /*
> diff --git a/migration/trace-events b/migration/trace-events
> index ab2e1e4..3a74f91 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -202,6 +202,12 @@ save_xbzrle_page_overflow(void) ""
> ram_save_iterate_big_wait(uint64_t milliconds, int iterations) "big wait: %"
> PRIu64 " milliseconds, %d iterations"
> ram_load_complete(int ret, uint64_t seq_iter) "exit_code %d seq iteration %"
> PRIu64
> get_mem_fault_cpu_index(uint32_t pid) "pid %u is not vCPU"
> +observe_thread_status(int ptid, char *name, char *status) "host_tid %d %s %s"
> +vcpu_state(int cpu_index, int is_running) "cpu %d running %d"
> +proc_line_cb(const char *str) "%s"
> +get_proc_file(const char *str) "opened %s"
> +observe_thread_begin(const char *str) "%s"
> +observe_thread_end(const char *str) "%s"
>
> # migration/exec.c
> migration_exec_outgoing(const char *cmd) "cmd=%s"
> --
> 1.8.3.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
