show_freeze will never show U due to most recent commit

[annonch]

With the change to unfreeze_time function in time.c ,

• tsk->freeze_start_nsec = 0;

• /* current unfreeze may not be the last one */
• tsk->freeze_start_nsec = now;

need new boolean variable in tsk

[littlepretty]

Hi Chris,

After almost 8 month of delay, I finally have my answer here.
So the generic form of the problem really is, what should we deal with the case of "F->F->F->...->F->U->U->U->..."?
The answer I think make sense, which is implemented by the latest commit, is the frozen duration should/must be the first F up to the first U. The reason is we have to send SIGSTOP signal at the first F, and SIGCONT signal at the first U. Even if we can calculate the time duration between the last F and the last U, it is not the time that a process paused.
My implementation is as follows:

/**
 * Freeze a group of processes, only call on group leader
 * This is a "last freeze count" implementation. If you call
 * F -> F -> F -> U, tsk->freeze_past_nsec will be the duration
 * from the first F to U
 */
void freeze_time(struct task_struct *tsk)
{
	struct timespec ts;
	s64 now;

        if (tsk->freeze_start_nsec > 0) return;

        /* signal STOP to freeze this @tsk's children */;
        kill_pgrp(task_pid(tsk), SIGSTOP, 1);
        __getnstimeofday(&ts);
        now = timespec_to_ns(&ts);
        /**
         * freeze_past_nsec is accumulated frozen duration,
         * so we MUST NOT zero it here
         */
        tsk->freeze_start_nsec = now;
}

/**
 * Unfreeze a group of processes, only call on group leader.
 * This is a last unfreeze count implementation. If you call
 * F -> U -> U -> U, the tsk->freeze_past_nsec will be
 * the duration from F to the first U
 */
void unfreeze_time(struct task_struct *tsk)
{
	struct timespec ts;
	s64 now;
        
        if (tsk->freeze_start_nsec == 0) return;

	__getnstimeofday(&ts);
	now = timespec_to_ns(&ts);
	tsk->freeze_past_nsec += (now - tsk->freeze_start_nsec);

	tsk->freeze_start_nsec = 0;
        populate_frozen_time(tsk);
        /* signal CONT to unfreeze @tsk's children after timekeeping */
	kill_pgrp(task_pid(tsk), SIGCONT, 1);
}

Best,
Jiaqi