Commit 5f3e3101 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Anthony Liguori
Browse files

timers: fix stop/cont with -icount 



Stop/cont commands are broken with -icount due to a deadlock.  The
real problem is that the computation of timers_state.cpu_ticks_offset
makes no sense with -icount enabled: we set it to an icount clock value
in cpu_disable_ticks, and subtract a TSC (or similar, whatever
cpu_get_real_ticks happens to return) value in cpu_enable_ticks.

The fix is simple.  timers_state.cpu_ticks_offset is only used
together with cpu_get_real_ticks, so we can use cpu_get_real_ticks
in cpu_disable_ticks.  There is no need to update cpu_ticks_prev
at the time cpu_disable_ticks is called; instead, we can do it
the next time cpu_get_ticks is called.

The change to cpu_disable_ticks is the important part of the patch.
The rest modifies the code to always check timers_state.cpu_ticks_prev,
even when the ticks are not advancing (i.e. the VM is stopped).  It also
makes a similar change to cpu_get_clock_locked, so that the code remains
similar for cpu_get_ticks and cpu_get_clock_locked.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1382977938-13844-1-git-send-email-pbonzini@redhat.com
Signed-off-by: default avatarAnthony Liguori <aliguori@amazon.com>
parent cd5be582

cpus.c

+22 −20
Original line number Diff line number Diff line
@@ -165,36 +165,38 @@ int64_t cpu_get_icount(void) 
/* Caller must hold the BQL */

int64_t cpu_get_ticks(void)

{

    int64_t ticks;



    if (use_icount) {

        return cpu_get_icount();

    }

    if (!timers_state.cpu_ticks_enabled) {

        return timers_state.cpu_ticks_offset;

    } else {

        int64_t ticks;

        ticks = cpu_get_real_ticks();



    ticks = timers_state.cpu_ticks_offset;

    if (timers_state.cpu_ticks_enabled) {

        ticks += cpu_get_real_ticks();

    }



    if (timers_state.cpu_ticks_prev > ticks) {

        /* Note: non increasing ticks may happen if the host uses

           software suspend */

        timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;

        ticks = timers_state.cpu_ticks_prev;

    }



    timers_state.cpu_ticks_prev = ticks;

        return ticks + timers_state.cpu_ticks_offset;

    }

    return ticks;

}



static int64_t cpu_get_clock_locked(void)

{

    int64_t ti;

    int64_t ticks;



    if (!timers_state.cpu_ticks_enabled) {

        ti = timers_state.cpu_clock_offset;

    } else {

        ti = get_clock();

        ti += timers_state.cpu_clock_offset;

    ticks = timers_state.cpu_clock_offset;

    if (timers_state.cpu_ticks_enabled) {

        ticks += get_clock();

    }



    return ti;

    return ticks;

}



/* return the host CPU monotonic timer and handle stop/restart */
@@ -235,7 +237,7 @@ void cpu_disable_ticks(void) 
    /* Here, the really thing protected by seqlock is cpu_clock_offset. */

    seqlock_write_lock(&timers_state.vm_clock_seqlock);

    if (timers_state.cpu_ticks_enabled) {

        timers_state.cpu_ticks_offset = cpu_get_ticks();

        timers_state.cpu_ticks_offset += cpu_get_real_ticks();

        timers_state.cpu_clock_offset = cpu_get_clock_locked();

        timers_state.cpu_ticks_enabled = 0;

    }