> * Liang Li (liang.z...@intel.com) wrote:
> > Recently, a bug related to multiple thread compression feature for
> > live migration is reported. The destination side will be blocked
> > during live migration if there are heavy workload in host and memory
> > intensive workload in guest, this is most likely to happen when there
> > is one decompression thread.
> >
> > Some parts of the decompression code are incorrect:
> > 1. The main thread receives data from source side will enter a busy
> > loop to wait for a free decompression thread.
> > 2. A lock is needed to protect the decomp_param[idx]->start, because
> > it is checked in the main thread and is updated in the decompression
> > thread.
> >
> > Fix these two issues by following the code pattern for compression.
> >
>
> OK, I think that's an improvement - but I have a question.
> Since it's an improvement (and basically now the same as compress):
>
> Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
>
> however, my question is:
> What guarantee's that all of the decompression has finished by the time the
> VM is started? I see in migration/migration.c that we have:
>
> if (!global_state_received() ||
> global_state_get_runstate() == RUN_STATE_RUNNING) {
> if (autostart) {
> vm_start();
> } else {
> runstate_set(RUN_STATE_PAUSED);
> }
> } else {
> runstate_set(global_state_get_runstate());
> }
> migrate_decompress_threads_join();
>
> so I guess that join ensures we have decompressed everything - but that
> needs to happen before we do the vm_start, not after - actually we need to
> make sure the decompress of RAM has happened before we start loading
> any of the other devices (since they may read from RAM).
>
> So, do we need something at the end of ram_load() ?
>
Yes, We should make sure all the decompression has been finished before
vm_start().
I really did that long ago in the POC code, I couldn't remember why the
related code was
missed in the upstream code. I will submit another patch for this.
Thanks!
Liang
> Dave
>
> > Reported-by: Daniel P. Berrange <berra...@redhat.com>
> > Signed-off-by: Liang Li <liang.z...@intel.com>
> > ---
> > migration/ram.c | 38 +++++++++++++++++++++++++++-----------
> > 1 file changed, 27 insertions(+), 11 deletions(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c index 3f05738..7ab6ab5
> > 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -263,6 +263,7 @@ typedef struct CompressParam CompressParam;
> >
> > struct DecompressParam {
> > bool start;
> > + bool done;
> > QemuMutex mutex;
> > QemuCond cond;
> > void *des;
> > @@ -287,6 +288,8 @@ static bool quit_comp_thread; static bool
> > quit_decomp_thread; static DecompressParam *decomp_param; static
> > QemuThread *decompress_threads;
> > +static QemuMutex decomp_done_lock;
> > +static QemuCond decomp_done_cond;
> >
> > static int do_compress_ram_page(CompressParam *param);
> >
> > @@ -834,6 +837,7 @@ static inline void
> start_compression(CompressParam
> > *param)
> >
> > static inline void start_decompression(DecompressParam *param) {
> > + param->done = false;
> > qemu_mutex_lock(¶m->mutex);
> > param->start = true;
> > qemu_cond_signal(¶m->cond);
> > @@ -2193,19 +2197,24 @@ static void *do_data_decompress(void
> *opaque)
> > qemu_mutex_lock(¶m->mutex);
> > while (!param->start && !quit_decomp_thread) {
> > qemu_cond_wait(¶m->cond, ¶m->mutex);
> > + }
> > + if (!quit_decomp_thread) {
> > pagesize = TARGET_PAGE_SIZE;
> > - if (!quit_decomp_thread) {
> > - /* uncompress() will return failed in some case, especially
> > - * when the page is dirted when doing the compression, it's
> > - * not a problem because the dirty page will be
> > retransferred
> > - * and uncompress() won't break the data in other pages.
> > - */
> > - uncompress((Bytef *)param->des, &pagesize,
> > - (const Bytef *)param->compbuf, param->len);
> > - }
> > - param->start = false;
> > + /* uncompress() will return failed in some case, especially
> > + * when the page is dirted when doing the compression, it's
> > + * not a problem because the dirty page will be retransferred
> > + * and uncompress() won't break the data in other pages.
> > + */
> > + uncompress((Bytef *)param->des, &pagesize,
> > + (const Bytef *)param->compbuf, param->len);
> > }
> > + param->start = false;
> > qemu_mutex_unlock(¶m->mutex);
> > +
> > + qemu_mutex_lock(&decomp_done_lock);
> > + param->done = true;
> > + qemu_cond_signal(&decomp_done_cond);
> > + qemu_mutex_unlock(&decomp_done_lock);
> > }
> >
> > return NULL;
> > @@ -2219,10 +2228,13 @@ void
> migrate_decompress_threads_create(void)
> > decompress_threads = g_new0(QemuThread, thread_count);
> > decomp_param = g_new0(DecompressParam, thread_count);
> > quit_decomp_thread = false;
> > + qemu_mutex_init(&decomp_done_lock);
> > + qemu_cond_init(&decomp_done_cond);
> > for (i = 0; i < thread_count; i++) {
> > qemu_mutex_init(&decomp_param[i].mutex);
> > qemu_cond_init(&decomp_param[i].cond);
> > decomp_param[i].compbuf =
> > g_malloc0(compressBound(TARGET_PAGE_SIZE));
> > + decomp_param[i].done = true;
> > qemu_thread_create(decompress_threads + i, "decompress",
> > do_data_decompress, decomp_param + i,
> > QEMU_THREAD_JOINABLE); @@ -2258,9 +2270,10
> > @@ static void decompress_data_with_multi_threads(QEMUFile *f,
> > int idx, thread_count;
> >
> > thread_count = migrate_decompress_threads();
> > + qemu_mutex_lock(&decomp_done_lock);
> > while (true) {
> > for (idx = 0; idx < thread_count; idx++) {
> > - if (!decomp_param[idx].start) {
> > + if (decomp_param[idx].done) {
> > qemu_get_buffer(f, decomp_param[idx].compbuf, len);
> > decomp_param[idx].des = host;
> > decomp_param[idx].len = len; @@ -2270,8 +2283,11 @@
> > static void decompress_data_with_multi_threads(QEMUFile *f,
> > }
> > if (idx < thread_count) {
> > break;
> > + } else {
> > + qemu_cond_wait(&decomp_done_cond, &decomp_done_lock);
> > }
> > }
> > + qemu_mutex_unlock(&decomp_done_lock);
> > }
> >
> > /*
> > --
> > 1.9.1
> >
> --
> Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
