[v3] block: Add VFIO based driver for NVMe device

[Qemu-devel] [PATCH v3 3/6] block: Introduce bdrv_dma_map and bdrv_dma_unmap

Posted by Fam Zheng 8 years, 7 months ago

Allow block driver to map and unmap a buffer for later I/O, as a performance
hint.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/block-backend.c          | 10 ++++++++++
 block/io.c                     | 24 ++++++++++++++++++++++++
 include/block/block.h          |  2 ++
 include/block/block_int.h      |  4 ++++
 include/sysemu/block-backend.h |  3 +++
 5 files changed, 43 insertions(+)

diff --git a/block/block-backend.c b/block/block-backend.c
index 0df3457..784b936 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1974,3 +1974,13 @@ static void blk_root_drained_end(BdrvChild *child)
         }
     }
 }
+
+void blk_dma_map(BlockBackend *blk, void *host, size_t size)
+{
+    bdrv_dma_map(blk_bs(blk), host, size);
+}
+
+void blk_dma_unmap(BlockBackend *blk, void *host)
+{
+    bdrv_dma_unmap(blk_bs(blk), host);
+}
diff --git a/block/io.c b/block/io.c
index 2de7c77..988e4db 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2537,3 +2537,27 @@ void bdrv_io_unplug(BlockDriverState *bs)
         bdrv_io_unplug(child->bs);
     }
 }
+
+void bdrv_dma_map(BlockDriverState *bs, void *host, size_t size)
+{
+    BdrvChild *child;
+
+    if (bs->drv && bs->drv->bdrv_dma_map) {
+        bs->drv->bdrv_dma_map(bs, host, size);
+    }
+    QLIST_FOREACH(child, &bs->children, next) {
+        bdrv_dma_map(child->bs, host, size);
+    }
+}
+
+void bdrv_dma_unmap(BlockDriverState *bs, void *host)
+{
+    BdrvChild *child;
+
+    if (bs->drv && bs->drv->bdrv_dma_unmap) {
+        bs->drv->bdrv_dma_unmap(bs, host);
+    }
+    QLIST_FOREACH(child, &bs->children, next) {
+        bdrv_dma_unmap(child->bs, host);
+    }
+}
diff --git a/include/block/block.h b/include/block/block.h
index 4c149ad..f59b50a 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -624,4 +624,6 @@ void bdrv_add_child(BlockDriverState *parent, BlockDriverState *child,
                     Error **errp);
 void bdrv_del_child(BlockDriverState *parent, BdrvChild *child, Error **errp);
 
+void bdrv_dma_map(BlockDriverState *bs, void *host, size_t size);
+void bdrv_dma_unmap(BlockDriverState *bs, void *host);
 #endif
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 15fa602..4092669 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -381,6 +381,10 @@ struct BlockDriver {
                              uint64_t parent_perm, uint64_t parent_shared,
                              uint64_t *nperm, uint64_t *nshared);
 
+    /* Map and unmap a buffer for I/O, as a performance hint to the
+     * driver. */
+    void (*bdrv_dma_map)(BlockDriverState *bs, void *host, size_t size);
+    void (*bdrv_dma_unmap)(BlockDriverState *bs, void *host);
     QLIST_ENTRY(BlockDriver) list;
 };
 
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 1e05281..5f7ccdb 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -239,4 +239,7 @@ void blk_io_limits_disable(BlockBackend *blk);
 void blk_io_limits_enable(BlockBackend *blk, const char *group);
 void blk_io_limits_update_group(BlockBackend *blk, const char *group);
 
+void blk_dma_map(BlockBackend *blk, void *host, size_t size);
+void blk_dma_unmap(BlockBackend *blk, void *host);
+
 #endif
-- 
2.9.4

Re: [Qemu-devel] [PATCH v3 3/6] block: Introduce bdrv_dma_map and bdrv_dma_unmap

Posted by Stefan Hajnoczi 8 years, 7 months ago

On Wed, Jul 05, 2017 at 09:36:32PM +0800, Fam Zheng wrote:
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 15fa602..4092669 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -381,6 +381,10 @@ struct BlockDriver {
>                               uint64_t parent_perm, uint64_t parent_shared,
>                               uint64_t *nperm, uint64_t *nshared);
>  
> +    /* Map and unmap a buffer for I/O, as a performance hint to the
> +     * driver. */
> +    void (*bdrv_dma_map)(BlockDriverState *bs, void *host, size_t size);
> +    void (*bdrv_dma_unmap)(BlockDriverState *bs, void *host);

It's unclear what this API does and how to use it correctly.  Please
flesh out the doc comments a bit to explain its use.

Re: [Qemu-devel] [PATCH v3 3/6] block: Introduce bdrv_dma_map and bdrv_dma_unmap

Posted by Stefan Hajnoczi 8 years, 7 months ago

On Wed, Jul 05, 2017 at 09:36:32PM +0800, Fam Zheng wrote:
> Allow block driver to map and unmap a buffer for later I/O, as a performance
> hint.

The name blk_dma_map() is confusing since other "dma" APIs like
dma_addr_t and dma_blk_io() deal with guest physical addresses instead
of host addresses.  They are about DMA to/from guest RAM.

Have you considered hiding this cached mapping in block/nvme.c so that
it isn't exposed?  block/nvme.c could keep the last buffer mapped and
callers would get the performance benefit without a new blk_dma_map()
API.

Re: [Qemu-devel] [PATCH v3 3/6] block: Introduce bdrv_dma_map and bdrv_dma_unmap

Posted by Paolo Bonzini 8 years, 7 months ago

On 10/07/2017 17:07, Stefan Hajnoczi wrote:
> On Wed, Jul 05, 2017 at 09:36:32PM +0800, Fam Zheng wrote:
>> Allow block driver to map and unmap a buffer for later I/O, as a performance
>> hint.
> The name blk_dma_map() is confusing since other "dma" APIs like
> dma_addr_t and dma_blk_io() deal with guest physical addresses instead
> of host addresses.  They are about DMA to/from guest RAM.
> 
> Have you considered hiding this cached mapping in block/nvme.c so that
> it isn't exposed?  block/nvme.c could keep the last buffer mapped and
> callers would get the performance benefit without a new blk_dma_map()
> API.

One buffer is enough for qemu-img bench, but not for more complex cases
(e.g. fio).

Paolo