Re: [Qemu-devel] [PATCH v3 3/5] migration: use threaded workqueue for compression

[Dr. David Alan Gilbert]

* address@hidden (address@hidden) wrote:
> From: Xiao Guangrong <address@hidden>
> 
> Adapt the compression code to the threaded workqueue
> 
> Signed-off-by: Xiao Guangrong <address@hidden>
> ---
>  migration/ram.c | 308 
> ++++++++++++++++++++------------------------------------
>  1 file changed, 110 insertions(+), 198 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 7e7deec4d8..254c08f27b 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -57,6 +57,7 @@
>  #include "qemu/uuid.h"
>  #include "savevm.h"
>  #include "qemu/iov.h"
> +#include "qemu/threaded-workqueue.h"
>  
>  /***********************************************************/
>  /* ram save/restore */
> @@ -349,22 +350,6 @@ typedef struct PageSearchStatus PageSearchStatus;
>  
>  CompressionStats compression_counters;
>  
> -struct CompressParam {
> -    bool done;
> -    bool quit;
> -    bool zero_page;
> -    QEMUFile *file;
> -    QemuMutex mutex;
> -    QemuCond cond;
> -    RAMBlock *block;
> -    ram_addr_t offset;
> -
> -    /* internally used fields */
> -    z_stream stream;
> -    uint8_t *originbuf;
> -};
> -typedef struct CompressParam CompressParam;
> -
>  struct DecompressParam {
>      bool done;
>      bool quit;
> @@ -377,15 +362,6 @@ struct DecompressParam {
>  };
>  typedef struct DecompressParam DecompressParam;
>  
> -static CompressParam *comp_param;
> -static QemuThread *compress_threads;
> -/* comp_done_cond is used to wake up the migration thread when
> - * one of the compression threads has finished the compression.
> - * comp_done_lock is used to co-work with comp_done_cond.
> - */
> -static QemuMutex comp_done_lock;
> -static QemuCond comp_done_cond;
> -/* The empty QEMUFileOps will be used by file in CompressParam */
>  static const QEMUFileOps empty_ops = { };
>  
>  static QEMUFile *decomp_file;
> @@ -394,125 +370,6 @@ static QemuThread *decompress_threads;
>  static QemuMutex decomp_done_lock;
>  static QemuCond decomp_done_cond;
>  
> -static bool do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock 
> *block,
> -                                 ram_addr_t offset, uint8_t *source_buf);
> -
> -static void *do_data_compress(void *opaque)
> -{
> -    CompressParam *param = opaque;
> -    RAMBlock *block;
> -    ram_addr_t offset;
> -    bool zero_page;
> -
> -    qemu_mutex_lock(&param->mutex);
> -    while (!param->quit) {
> -        if (param->block) {
> -            block = param->block;
> -            offset = param->offset;
> -            param->block = NULL;
> -            qemu_mutex_unlock(&param->mutex);
> -
> -            zero_page = do_compress_ram_page(param->file, &param->stream,
> -                                             block, offset, 
> param->originbuf);
> -
> -            qemu_mutex_lock(&comp_done_lock);
> -            param->done = true;
> -            param->zero_page = zero_page;
> -            qemu_cond_signal(&comp_done_cond);
> -            qemu_mutex_unlock(&comp_done_lock);
> -
> -            qemu_mutex_lock(&param->mutex);
> -        } else {
> -            qemu_cond_wait(&param->cond, &param->mutex);
> -        }
> -    }
> -    qemu_mutex_unlock(&param->mutex);
> -
> -    return NULL;
> -}
> -
> -static void compress_threads_save_cleanup(void)
> -{
> -    int i, thread_count;
> -
> -    if (!migrate_use_compression() || !comp_param) {
> -        return;
> -    }
> -
> -    thread_count = migrate_compress_threads();
> -    for (i = 0; i < thread_count; i++) {
> -        /*
> -         * we use it as a indicator which shows if the thread is
> -         * properly init'd or not
> -         */
> -        if (!comp_param[i].file) {
> -            break;
> -        }
> -
> -        qemu_mutex_lock(&comp_param[i].mutex);
> -        comp_param[i].quit = true;
> -        qemu_cond_signal(&comp_param[i].cond);
> -        qemu_mutex_unlock(&comp_param[i].mutex);
> -
> -        qemu_thread_join(compress_threads + i);
> -        qemu_mutex_destroy(&comp_param[i].mutex);
> -        qemu_cond_destroy(&comp_param[i].cond);
> -        deflateEnd(&comp_param[i].stream);
> -        g_free(comp_param[i].originbuf);
> -        qemu_fclose(comp_param[i].file);
> -        comp_param[i].file = NULL;
> -    }
> -    qemu_mutex_destroy(&comp_done_lock);
> -    qemu_cond_destroy(&comp_done_cond);
> -    g_free(compress_threads);
> -    g_free(comp_param);
> -    compress_threads = NULL;
> -    comp_param = NULL;
> -}
> -
> -static int compress_threads_save_setup(void)
> -{
> -    int i, thread_count;
> -
> -    if (!migrate_use_compression()) {
> -        return 0;
> -    }
> -    thread_count = migrate_compress_threads();
> -    compress_threads = g_new0(QemuThread, thread_count);
> -    comp_param = g_new0(CompressParam, thread_count);
> -    qemu_cond_init(&comp_done_cond);
> -    qemu_mutex_init(&comp_done_lock);
> -    for (i = 0; i < thread_count; i++) {
> -        comp_param[i].originbuf = g_try_malloc(TARGET_PAGE_SIZE);
> -        if (!comp_param[i].originbuf) {
> -            goto exit;
> -        }
> -
> -        if (deflateInit(&comp_param[i].stream,
> -                        migrate_compress_level()) != Z_OK) {
> -            g_free(comp_param[i].originbuf);
> -            goto exit;
> -        }
> -
> -        /* comp_param[i].file is just used as a dummy buffer to save data,
> -         * set its ops to empty.
> -         */
> -        comp_param[i].file = qemu_fopen_ops(NULL, &empty_ops);
> -        comp_param[i].done = true;
> -        comp_param[i].quit = false;
> -        qemu_mutex_init(&comp_param[i].mutex);
> -        qemu_cond_init(&comp_param[i].cond);
> -        qemu_thread_create(compress_threads + i, "compress",
> -                           do_data_compress, comp_param + i,
> -                           QEMU_THREAD_JOINABLE);
> -    }
> -    return 0;
> -
> -exit:
> -    compress_threads_save_cleanup();
> -    return -1;
> -}
> -
>  /* Multiple fd's */
>  
>  #define MULTIFD_MAGIC 0x11223344U
> @@ -1909,12 +1766,25 @@ exit:
>      return zero_page;
>  }
>  
> +struct CompressData {
> +    /* filled by migration thread.*/
> +    RAMBlock *block;
> +    ram_addr_t offset;
> +
> +    /* filled by compress thread. */
> +    QEMUFile *file;
> +    z_stream stream;
> +    uint8_t *originbuf;
> +    bool zero_page;
> +};
> +typedef struct CompressData CompressData;
> +
>  static void
> -update_compress_thread_counts(const CompressParam *param, int bytes_xmit)
> +update_compress_thread_counts(CompressData *cd, int bytes_xmit)

Keep the const?
>  {
>      ram_counters.transferred += bytes_xmit;
>  
> -    if (param->zero_page) {
> +    if (cd->zero_page) {
>          ram_counters.duplicate++;
>          return;
>      }
> @@ -1924,81 +1794,123 @@ update_compress_thread_counts(const CompressParam 
> *param, int bytes_xmit)
>      compression_counters.pages++;
>  }
>  
> +static int compress_thread_data_init(void *request)
> +{
> +    CompressData *cd = request;
> +
> +    cd->originbuf = g_try_malloc(TARGET_PAGE_SIZE);
> +    if (!cd->originbuf) {
> +        return -1;
> +    }
> +
> +    if (deflateInit(&cd->stream, migrate_compress_level()) != Z_OK) {
> +        g_free(cd->originbuf);
> +        return -1;
> +    }

Please print errors if you fail in any case so we can easily tell what
happened.

> +    cd->file = qemu_fopen_ops(NULL, &empty_ops);
> +    return 0;
> +}
> +
> +static void compress_thread_data_fini(void *request)
> +{
> +    CompressData *cd = request;
> +
> +    qemu_fclose(cd->file);
> +    deflateEnd(&cd->stream);
> +    g_free(cd->originbuf);
> +}
> +
> +static void compress_thread_data_handler(void *request)
> +{
> +    CompressData *cd = request;
> +
> +    /*
> +     * if compression fails, it will be indicated by
> +     * migrate_get_current()->to_dst_file.
> +     */
> +    cd->zero_page = do_compress_ram_page(cd->file, &cd->stream, cd->block,
> +                                         cd->offset, cd->originbuf);
> +}
> +
> +static void compress_thread_data_done(void *request)
> +{
> +    CompressData *cd = request;
> +    RAMState *rs = ram_state;
> +    int bytes_xmit;
> +
> +    bytes_xmit = qemu_put_qemu_file(rs->f, cd->file);
> +    update_compress_thread_counts(cd, bytes_xmit);
> +}
> +
> +static const ThreadedWorkqueueOps compress_ops = {
> +    .thread_request_init = compress_thread_data_init,
> +    .thread_request_uninit = compress_thread_data_fini,
> +    .thread_request_handler = compress_thread_data_handler,
> +    .thread_request_done = compress_thread_data_done,
> +    .request_size = sizeof(CompressData),
> +};
> +
> +static Threads *compress_threads;
> +
>  static bool save_page_use_compression(RAMState *rs);
>  
>  static void flush_compressed_data(RAMState *rs)
>  {
> -    int idx, len, thread_count;
> -
>      if (!save_page_use_compression(rs)) {
>          return;
>      }
> -    thread_count = migrate_compress_threads();
>  
> -    qemu_mutex_lock(&comp_done_lock);
> -    for (idx = 0; idx < thread_count; idx++) {
> -        while (!comp_param[idx].done) {
> -            qemu_cond_wait(&comp_done_cond, &comp_done_lock);
> -        }
> -    }
> -    qemu_mutex_unlock(&comp_done_lock);
> +    threaded_workqueue_wait_for_requests(compress_threads);
> +}
>  
> -    for (idx = 0; idx < thread_count; idx++) {
> -        qemu_mutex_lock(&comp_param[idx].mutex);
> -        if (!comp_param[idx].quit) {
> -            len = qemu_put_qemu_file(rs->f, comp_param[idx].file);
> -            /*
> -             * it's safe to fetch zero_page without holding comp_done_lock
> -             * as there is no further request submitted to the thread,
> -             * i.e, the thread should be waiting for a request at this point.
> -             */
> -            update_compress_thread_counts(&comp_param[idx], len);
> -        }
> -        qemu_mutex_unlock(&comp_param[idx].mutex);
> +static void compress_threads_save_cleanup(void)
> +{
> +    if (!compress_threads) {
> +        return;
>      }
> +
> +    threaded_workqueue_destroy(compress_threads);
> +    compress_threads = NULL;
>  }
>  
> -static inline void set_compress_params(CompressParam *param, RAMBlock *block,
> -                                       ram_addr_t offset)
> +static int compress_threads_save_setup(void)
>  {
> -    param->block = block;
> -    param->offset = offset;
> +    if (!migrate_use_compression()) {
> +        return 0;
> +    }
> +
> +    compress_threads = threaded_workqueue_create("compress",
> +                                migrate_compress_threads(),
> +                                DEFAULT_THREAD_REQUEST_NR, &compress_ops);
> +    return compress_threads ? 0 : -1;
>  }
>  
>  static int compress_page_with_multi_thread(RAMState *rs, RAMBlock *block,
>                                             ram_addr_t offset)
>  {
> -    int idx, thread_count, bytes_xmit = -1, pages = -1;
> +    CompressData *cd;
>      bool wait = migrate_compress_wait_thread();
>  
> -    thread_count = migrate_compress_threads();
> -    qemu_mutex_lock(&comp_done_lock);
>  retry:
> -    for (idx = 0; idx < thread_count; idx++) {
> -        if (comp_param[idx].done) {
> -            comp_param[idx].done = false;
> -            bytes_xmit = qemu_put_qemu_file(rs->f, comp_param[idx].file);
> -            qemu_mutex_lock(&comp_param[idx].mutex);
> -            set_compress_params(&comp_param[idx], block, offset);
> -            qemu_cond_signal(&comp_param[idx].cond);
> -            qemu_mutex_unlock(&comp_param[idx].mutex);
> -            pages = 1;
> -            update_compress_thread_counts(&comp_param[idx], bytes_xmit);
> -            break;
> +    cd = threaded_workqueue_get_request(compress_threads);
> +    if (!cd) {
> +        /*
> +         * wait for the free thread if the user specifies
> +         * 'compress-wait-thread', otherwise we will post
> +         *  the page out in the main thread as normal page.
> +         */
> +        if (wait) {
> +            cpu_relax();
> +            goto retry;

Is there nothing better we can use to wait without eating CPU time?

Dave

>          }
> -    }
>  
> -    /*
> -     * wait for the free thread if the user specifies 'compress-wait-thread',
> -     * otherwise we will post the page out in the main thread as normal page.
> -     */
> -    if (pages < 0 && wait) {
> -        qemu_cond_wait(&comp_done_cond, &comp_done_lock);
> -        goto retry;
> -    }
> -    qemu_mutex_unlock(&comp_done_lock);
> -
> -    return pages;
> +        return -1;
> +     }
> +    cd->block = block;
> +    cd->offset = offset;
> +    threaded_workqueue_submit_request(compress_threads, cd);
> +    return 1;
>  }
>  
>  /**
> -- 
> 2.14.5
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK