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| author | Andrey Shinkevich | 2020-12-16 07:16:58 +0100 |
|---|---|---|
| committer | Max Reitz | 2021-01-26 14:36:37 +0100 |
| commit | e275458b29b7040a388ca46af094b0602c769ef1 (patch) | |
| tree | 713c8753f608579d3e08bd138e92ce322a0c9059 | |
| parent | block: include supported_read_flags into BDS structure (diff) | |
| download | qemu-e275458b29b7040a388ca46af094b0602c769ef1.tar.gz qemu-e275458b29b7040a388ca46af094b0602c769ef1.tar.xz qemu-e275458b29b7040a388ca46af094b0602c769ef1.zip | |
copy-on-read: skip non-guest reads if no copy needed
If the flag BDRV_REQ_PREFETCH was set, skip idling read/write
operations in COR-driver. It can be taken into account for the
COR-algorithms optimization. That check is being made during the
block stream job by the moment.
Add the BDRV_REQ_PREFETCH flag to the supported_read_flags of the
COR-filter.
block: Modify the comment for the flag BDRV_REQ_PREFETCH as we are
going to use it alone and pass it to the COR-filter driver for further
processing.
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20201216061703.70908-9-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
| -rw-r--r-- | block/copy-on-read.c | 14 | ||||
| -rw-r--r-- | include/block/block.h | 8 |
2 files changed, 15 insertions, 7 deletions
diff --git a/block/copy-on-read.c b/block/copy-on-read.c index 71560984f6..9cad9e1b8c 100644 --- a/block/copy-on-read.c +++ b/block/copy-on-read.c @@ -50,6 +50,8 @@ static int cor_open(BlockDriverState *bs, QDict *options, int flags, return -EINVAL; } + bs->supported_read_flags = BDRV_REQ_PREFETCH; + bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED | (BDRV_REQ_FUA & bs->file->bs->supported_write_flags); @@ -172,10 +174,14 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs, } } - ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset, - local_flags); - if (ret < 0) { - return ret; + /* Skip if neither read nor write are needed */ + if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) != + BDRV_REQ_PREFETCH) { + ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset, + local_flags); + if (ret < 0) { + return ret; + } } offset += n; diff --git a/include/block/block.h b/include/block/block.h index 127bdf3392..81fcaad5ac 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -72,9 +72,11 @@ typedef enum { BDRV_REQ_NO_FALLBACK = 0x100, /* - * BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_READ - * on read request and means that caller doesn't really need data to be - * written to qiov parameter which may be NULL. + * BDRV_REQ_PREFETCH makes sense only in the context of copy-on-read + * (i.e., together with the BDRV_REQ_COPY_ON_READ flag or when a COR + * filter is involved), in which case it signals that the COR operation + * need not read the data into memory (qiov) but only ensure they are + * copied to the top layer (i.e., that COR operation is done). */ BDRV_REQ_PREFETCH = 0x200, |