On Thu, 05/26 14:50, Fam Zheng wrote:
> On Tue, 05/24 16:30, Peter Lieven wrote:
> > in a read-modify-write cycle a small request might cause
> > head and tail to fall into the same aligned block. Currently
> > QEMU reads the same block twice in this case which is
> > not necessary.
> >
> > Signed-off-by: Peter Lieven <[email protected]>
>
> Thanks, applied to my block branch:
>
> https://github.com/famz/qemu/tree/block
>
Looks like this breaks iotests 077 (hang), the blkdebug break points expected
by the script are not hit now. While squashing in below patch fixes the case, I
think it is more appropriate to keep the patch as is and fix the case itself.
Dropped from my queue, please send another version with test case update so I
can apply together.
diff --git a/block/io.c b/block/io.c
index d480097..a6523cf 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1435,8 +1435,10 @@ int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
* than one aligned block.
*/
if (bytes < align) {
+ bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_TAIL);
qemu_iovec_add(&local_qiov, head_buf + bytes, align - bytes);
bytes = align;
+ bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_AFTER_TAIL);
}
}
