From 99136607b1edb0129d1ebb6ecac21738ad3d9c36 Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Thu, 25 Jul 2019 13:05:49 +0300 Subject: block/stream: use BDRV_REQ_PREFETCH This helps to avoid extra io, allocations and memory copying. Signed-off-by: Vladimir Sementsov-Ogievskiy Message-Id: <20190725100550.33801-3-vsementsov@virtuozzo.com> Reviewed-by: Stefan Hajnoczi [eblake: fix comment grammar] Signed-off-by: Eric Blake --- block/stream.c | 24 +++++++++--------------- 1 file changed, 9 insertions(+), 15 deletions(-) (limited to 'block/stream.c') diff --git a/block/stream.c b/block/stream.c index 6ac1e7bec4..0d3a6ac7c3 100644 --- a/block/stream.c +++ b/block/stream.c @@ -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; } -- cgit v1.2.3