Re: [Qemu-devel] [v4 10/13] migration: Add the core code for decompression

[Dr. David Alan Gilbert]

* Liang Li (address@hidden) wrote:
> Implement the core logic of multiple thread decompression,
> the decompression can work now.
> 
> Signed-off-by: Liang Li <address@hidden>
> Signed-off-by: Yang Zhang <address@hidden>
> ---
>  arch_init.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 8ef0315..549fdbb 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -814,6 +814,13 @@ static inline void start_compression(CompressParam 
> *param)
>      qemu_mutex_unlock(&param->mutex);
>  }
>  
> +static inline void start_decompression(DecompressParam *param)
> +{
> +    qemu_mutex_lock(&param->mutex);
> +    param->busy = true;
> +    qemu_cond_signal(&param->cond);
> +    qemu_mutex_unlock(&param->mutex);
> +}
>  
>  static uint64_t bytes_transferred;
>  
> @@ -1347,8 +1354,27 @@ void ram_handle_compressed(void *host, uint8_t ch, 
> uint64_t size)
>  
>  static void *do_data_decompress(void *opaque)
>  {
> +    DecompressParam *param = opaque;
> +    size_t pagesize;
> +
>      while (!quit_thread) {
> -        /* To be done */
> +        qemu_mutex_lock(&param->mutex);
> +        while (!param->busy) {
> +            qemu_cond_wait(&param->cond, &param->mutex);
> +            if (quit_thread) {
> +                break;
> +            }
> +            pagesize = TARGET_PAGE_SIZE;
> +            /* 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->busy = false;
> +        }
> +        qemu_mutex_unlock(&param->mutex);
>      }

Again, similar question to the compress thread; what ensures that
teh cond_signal for quit_thread happens while this loop is at
the cond_wait? Again mainly in error cases.

Dave

>  
>      return NULL;
> @@ -1379,6 +1405,9 @@ void migrate_decompress_threads_join(void)
>      quit_thread = true;
>      thread_count = migrate_decompress_threads();
>      for (i = 0; i < thread_count; i++) {
> +        qemu_cond_signal(&decomp_param[i].cond);
> +    }
> +    for (i = 0; i < thread_count; i++) {
>          qemu_thread_join(decompress_threads + i);
>          qemu_mutex_destroy(&decomp_param[i].mutex);
>          qemu_cond_destroy(&decomp_param[i].cond);
> @@ -1395,7 +1424,23 @@ void migrate_decompress_threads_join(void)
>  static void decompress_data_with_multi_threads(uint8_t *compbuf,
>                                                 void *host, int len)
>  {
> -    /* To be done */
> +    int idx, thread_count;
> +
> +    thread_count = migrate_decompress_threads();
> +    while (true) {
> +        for (idx = 0; idx < thread_count; idx++) {
> +            if (!decomp_param[idx].busy) {
> +                memcpy(decomp_param[idx].compbuf, compbuf, len);
> +                decomp_param[idx].des = host;
> +                decomp_param[idx].len = len;
> +                start_decompression(&decomp_param[idx]);
> +                break;
> +            }
> +        }
> +        if (idx < thread_count) {
> +            break;
> +        }
> +    }
>  }
>  
>  static int ram_load(QEMUFile *f, void *opaque, int version_id)
> -- 
> 1.9.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK