On 07.10.2020 13:06, Vladimir Sementsov-Ogievskiy wrote:
29.09.2020 15:38, Andrey Shinkevich wrote:
If the flag BDRV_REQ_PREFETCH was set, pass it further to the
COR-driver to skip unneeded reading. It can be taken into account for
the COR-algorithms optimization. That check is being made during the
block stream job by the moment.
Signed-off-by: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>
---
block/copy-on-read.c | 14 ++++++++++----
block/io.c | 2 +-
2 files changed, 11 insertions(+), 5 deletions(-)
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index f53f7e0..5389dca 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -145,10 +145,16 @@ 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;
+ if ((flags & BDRV_REQ_PREFETCH) &
BDRV_REQ_PREFETCH is documented to be only used with
BDRV_REQ_COPY_ON_READ. But here
BDRV_REQ_COPY_ON_READ appears intermediately. We should change
documentation in block.h
in a separate patch (and probably code in bdrv_aligned_preadv())
OK, we will come here without the BDRV_REQ_PREFETCH flag set.
To differ between guest reads and the stream job ones, we would set it
here by checking for the qiov NULL pointer:
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 4e3b1c5..df2c2ab 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -144,6 +144,9 @@ static int coroutine_fn
cor_co_preadv_part(BlockDriverState *bs,
n, &n);
if (ret) {
local_flags |= BDRV_REQ_COPY_ON_READ;
+ if (!qiov) {
+ local_flags |= BDRV_REQ_PREFETCH;
+ }
}
}
Andrey
+ !(local_flags & BDRV_REQ_COPY_ON_READ)) {
+ /* Skip non-guest reads if no copy needed */
+ } else {
+
extra new-line ?
+ ret = bdrv_co_preadv_part(bs->file, offset, n, qiov,
qiov_offset,
+ local_flags);
+ if (ret < 0) {
+ return ret;
+ }
}
offset += n;
diff --git a/block/io.c b/block/io.c
index 11df188..62b75a5 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1388,7 +1388,7 @@ static int coroutine_fn jk(BdrvChild *child,
qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
ret = bdrv_driver_preadv(bs, cluster_offset, pnum,
- &local_qiov, 0, 0);
+ &local_qiov, 0, flags &
BDRV_REQ_PREFETCH);
Why? In this place we want to read. We'll write back the data a few
lines below. What will we write,
if underlying driver decide to do nothing because of BDRV_REQ_PREFETCH?
See my comment above please.
if (ret < 0) {
goto err;
}