Commit 99136607 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Eric Blake
Browse files

block/stream: use BDRV_REQ_PREFETCH 



This helps to avoid extra io, allocations and memory copying.

Signed-off-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190725100550.33801-3-vsementsov@virtuozzo.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
[eblake: fix comment grammar]
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
parent 3299e5ec

block/stream.c

+9 −15
Original line number Diff line number Diff line
@@ -22,11 +22,11 @@ 


enum {

    /*

     * Size of data buffer for populating the image file.  This should be large

     * enough to process multiple clusters in a single call, so that populating

     * contiguous regions of the image is efficient.

     * Maximum chunk size to feed to copy-on-read.  This should be

     * large enough to process multiple clusters in a single call, so

     * that populating contiguous regions of the image is efficient.

     */

    STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */

    STREAM_CHUNK = 512 * 1024, /* in bytes */

};



typedef struct StreamBlockJob {
@@ -39,13 +39,12 @@ typedef struct StreamBlockJob { 
} StreamBlockJob;



static int coroutine_fn stream_populate(BlockBackend *blk,

                                        int64_t offset, uint64_t bytes,

                                        void *buf)

                                        int64_t offset, uint64_t bytes)

{

    assert(bytes < SIZE_MAX);



    /* Copy-on-read the unallocated clusters */

    return blk_co_pread(blk, offset, bytes, buf, BDRV_REQ_COPY_ON_READ);

    return blk_co_preadv(blk, offset, bytes, NULL,

                         BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);

}



static void stream_abort(Job *job)
@@ -117,7 +116,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp) 
    int error = 0;

    int ret = 0;

    int64_t n = 0; /* bytes */

    void *buf;



    if (bs == s->bottom) {

        /* Nothing to stream */
@@ -130,8 +128,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp) 
    }

    job_progress_set_remaining(&s->common.job, len);



    buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);



    /* Turn on copy-on-read for the whole block device so that guest read

     * requests help us make progress.  Only do this when copying the entire

     * backing chain since the copy-on-read operation does not take base into
@@ -154,7 +150,7 @@ static int coroutine_fn stream_run(Job *job, Error **errp) 


        copy = false;



        ret = bdrv_is_allocated(bs, offset, STREAM_BUFFER_SIZE, &n);

        ret = bdrv_is_allocated(bs, offset, STREAM_CHUNK, &n);

        if (ret == 1) {

            /* Allocated in the top, no need to copy.  */

        } else if (ret >= 0) {
@@ -171,7 +167,7 @@ static int coroutine_fn stream_run(Job *job, Error **errp) 
        }

        trace_stream_one_iteration(s, offset, n, ret);

        if (copy) {

            ret = stream_populate(blk, offset, n, buf);

            ret = stream_populate(blk, offset, n);

        }

        if (ret < 0) {

            BlockErrorAction action =
@@ -202,8 +198,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp) 
        bdrv_disable_copy_on_read(bs);

    }



    qemu_vfree(buf);



    /* Do not remove the backing file if an error was there but ignored. */

    return error;

}