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[Qemu-devel] [PULL 33/38] block: minimal bounce buffer alignment
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PULL 33/38] block: minimal bounce buffer alignment |
Date: |
Fri, 22 May 2015 10:02:05 +0100 |
From: "Denis V. Lunev" <address@hidden>
The patch introduces new concept: minimal memory alignment for bounce
buffers. Original so called "optimal" value is actually minimal required
value for aligment. It should be used for validation that the IOVec
is properly aligned and bounce buffer is not required.
Though, from the performance point of view, it would be better if
bounce buffer or IOVec allocated by QEMU will be aligned stricter.
The patch does not change any alignment value yet.
Signed-off-by: Denis V. Lunev <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
Message-id: address@hidden
CC: Paolo Bonzini <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
block.c | 11 +++++++++++
block/io.c | 7 ++++++-
block/raw-posix.c | 1 +
include/block/block.h | 2 ++
include/block/block_int.h | 3 +++
5 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/block.c b/block.c
index 7904098..e293907 100644
--- a/block.c
+++ b/block.c
@@ -113,6 +113,16 @@ size_t bdrv_opt_mem_align(BlockDriverState *bs)
return bs->bl.opt_mem_alignment;
}
+size_t bdrv_min_mem_align(BlockDriverState *bs)
+{
+ if (!bs || !bs->drv) {
+ /* 4k should be on the safe side */
+ return 4096;
+ }
+
+ return bs->bl.min_mem_alignment;
+}
+
/* check if the path starts with "<protocol>:" */
int path_has_protocol(const char *path)
{
@@ -890,6 +900,7 @@ static int bdrv_open_common(BlockDriverState *bs,
BlockDriverState *file,
}
assert(bdrv_opt_mem_align(bs) != 0);
+ assert(bdrv_min_mem_align(bs) != 0);
assert((bs->request_alignment != 0) || bs->sg);
return 0;
diff --git a/block/io.c b/block/io.c
index a05ad67..e6c3639 100644
--- a/block/io.c
+++ b/block/io.c
@@ -201,8 +201,10 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error
**errp)
}
bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
bs->bl.max_transfer_length = bs->file->bl.max_transfer_length;
+ bs->bl.min_mem_alignment = bs->file->bl.min_mem_alignment;
bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
} else {
+ bs->bl.min_mem_alignment = 512;
bs->bl.opt_mem_alignment = 512;
}
@@ -221,6 +223,9 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
bs->bl.opt_mem_alignment =
MAX(bs->bl.opt_mem_alignment,
bs->backing_hd->bl.opt_mem_alignment);
+ bs->bl.min_mem_alignment =
+ MAX(bs->bl.min_mem_alignment,
+ bs->backing_hd->bl.min_mem_alignment);
}
/* Then let the driver override it */
@@ -2489,7 +2494,7 @@ void *qemu_try_blockalign0(BlockDriverState *bs, size_t
size)
bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
{
int i;
- size_t alignment = bdrv_opt_mem_align(bs);
+ size_t alignment = bdrv_min_mem_align(bs);
for (i = 0; i < qiov->niov; i++) {
if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 24d8582..7083924 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -725,6 +725,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error
**errp)
BDRVRawState *s = bs->opaque;
raw_probe_alignment(bs, s->fd, errp);
+ bs->bl.min_mem_alignment = s->buf_align;
bs->bl.opt_mem_alignment = s->buf_align;
}
diff --git a/include/block/block.h b/include/block/block.h
index 7d1a717..c1c963e 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -440,6 +440,8 @@ void bdrv_img_create(const char *filename, const char *fmt,
/* Returns the alignment in bytes that is required so that no bounce buffer
* is required throughout the stack */
+size_t bdrv_min_mem_align(BlockDriverState *bs);
+/* Returns optimal alignment in bytes for bounce buffer */
size_t bdrv_opt_mem_align(BlockDriverState *bs);
void bdrv_set_guest_block_size(BlockDriverState *bs, int align);
void *qemu_blockalign(BlockDriverState *bs, size_t size);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index db29b74..f004378 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -313,6 +313,9 @@ typedef struct BlockLimits {
int max_transfer_length;
/* memory alignment so that no bounce buffer is needed */
+ size_t min_mem_alignment;
+
+ /* memory alignment for bounce buffer */
size_t opt_mem_alignment;
} BlockLimits;
--
2.1.0
- [Qemu-devel] [PULL 24/38] block/parallels: delay writing to BAT till bdrv_co_flush_to_os, (continued)
- [Qemu-devel] [PULL 24/38] block/parallels: delay writing to BAT till bdrv_co_flush_to_os, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 22/38] block/parallels: improve image reading performance, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 23/38] block/parallels: create bat_entry_off helper, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 26/38] block/parallels: optimize linear image expansion, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 28/38] configure: handle clang -nopie argument warning, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 27/38] block/parallels: improve image writing performance further, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 29/38] configure: factor out supported flag check, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 25/38] block/parallels: add prealloc-mode and prealloc-size open paramemets, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 30/38] configure: silence glib unknown attribute __alloc_size__, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 31/38] configure: Add workaround for ccache and clang, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 33/38] block: minimal bounce buffer alignment,
Stefan Hajnoczi <=
- [Qemu-devel] [PULL 34/38] block: align bounce buffers to page, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 35/38] Revert "block: Fix unaligned zero write", Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 32/38] block: return EPERM on writes or discards to read-only devices, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 38/38] block: get_block_status: use "else" when testing the opposite condition, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 37/38] qemu-iotests: Test unaligned sub-block zero write, Stefan Hajnoczi, 2015/05/22
- [Qemu-devel] [PULL 36/38] block: Fix NULL deference for unaligned write if qiov is NULL, Stefan Hajnoczi, 2015/05/22
- Re: [Qemu-devel] [PULL 00/38] Block patches, Peter Maydell, 2015/05/22