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[PATCH v14 08/13] copy-on-read: skip non-guest reads if no copy needed
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
[PATCH v14 08/13] copy-on-read: skip non-guest reads if no copy needed |
Date: |
Sat, 5 Dec 2020 01:07:53 +0300 |
From: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
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>
---
include/block/block.h | 8 +++++---
block/copy-on-read.c | 14 ++++++++++----
2 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/include/block/block.h b/include/block/block.h
index 81a3894129..3499554d9c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -81,9 +81,11 @@ 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,
/* Mask of valid flags */
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 67f61983c0..8b64e55e22 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -49,6 +49,8 @@ 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);
@@ -150,10 +152,14 @@ 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;
--
2.21.3
- Re: [PATCH v14 06/13] iotests: add #310 to test bottom node in COR driver, (continued)
[PATCH v14 09/13] stream: skip filters when writing backing file name to QCOW2 header, Vladimir Sementsov-Ogievskiy, 2020/12/04
[PATCH v14 05/13] qapi: create BlockdevOptionsCor structure for COR driver, Vladimir Sementsov-Ogievskiy, 2020/12/04
[PATCH v14 08/13] copy-on-read: skip non-guest reads if no copy needed,
Vladimir Sementsov-Ogievskiy <=
[PATCH v14 10/13] qapi: block-stream: add "bottom" argument, Vladimir Sementsov-Ogievskiy, 2020/12/04
[PATCH v14 12/13] block/stream: add s->target_bs, Vladimir Sementsov-Ogievskiy, 2020/12/04
[PATCH v14 11/13] iotests: 30: prepare to COR filter insertion by stream job, Vladimir Sementsov-Ogievskiy, 2020/12/04