Patchwork qemu-kvm: clear only essential parts of VirtIOBlockReq on object allocation - RESUBMIT

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Submitter Saul Tamari
Date Nov. 9, 2009, 6:04 p.m.
Message ID <41be791c0911091004x62d30fbey91ef730475ba3571@mail.gmail.com>
Download mbox | patch
Permalink /patch/38144/
State New
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Comments

Saul Tamari - Nov. 9, 2009, 6:04 p.m.
This patch reduces the size of memory being cleared on every virtio-blk IO.

Improve number of IOPS when using avirtio-blk device.

On every virtio-blk IO command passed to QEMU, virtio_blk_alloc_request()
allocates and clears (with qemu_mallocz()) a VirtIOBlockReq object.
The sizeof(VirtIOBlockReq) equals 41040 bytes on my x86-64 machine.
By moving the 'elem' variable to the end of VirtIOBlockReq and
clearing only upto the address of the 'elem.in_addr' field, the
memset() call now clears only 80 bytes.


Signed-off-by: Saul Tamari <stamari@gmail.com>
---

 static void virtio_blk_req_complete(VirtIOBlockReq *req, int status)
@@ -139,7 +140,8 @@ static void virtio_blk_flush_complete(void *opaque, int ret)

 static VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
 {
-    VirtIOBlockReq *req = qemu_mallocz(sizeof(*req));
+    VirtIOBlockReq *req = qemu_malloc(sizeof(*req));
+    memset(req, 0, offsetof(VirtIOBlockReq, elem.in_addr[0]));
     req->dev = s;
     return req;
 }
Anthony Liguori - Nov. 17, 2009, 7:39 p.m.
Saul Tamari wrote:
> This patch reduces the size of memory being cleared on every virtio-blk IO.
>
> Improve number of IOPS when using avirtio-blk device.
>
> On every virtio-blk IO command passed to QEMU, virtio_blk_alloc_request()
> allocates and clears (with qemu_mallocz()) a VirtIOBlockReq object.
> The sizeof(VirtIOBlockReq) equals 41040 bytes on my x86-64 machine.
> By moving the 'elem' variable to the end of VirtIOBlockReq and
> clearing only upto the address of the 'elem.in_addr' field, the
> memset() call now clears only 80 bytes.
>
>
> Signed-off-by: Saul Tamari <stamari@gmail.com>
> ---
>
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index 2630b99..de74b00 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -79,12 +79,13 @@ static inline void virtio_identify_template(struct
> virtio_blk_config *bc)
>   

This patch is whitespace damaged by your mailer.

Regards,

Anthony Liguori

Patch

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 2630b99..de74b00 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -79,12 +79,13 @@  static inline void virtio_identify_template(struct
virtio_blk_config *bc)
 typedef struct VirtIOBlockReq
 {
     VirtIOBlock *dev;
-    VirtQueueElement elem;
     struct virtio_blk_inhdr *in;
     struct virtio_blk_outhdr *out;
     struct virtio_scsi_inhdr *scsi;
     QEMUIOVector qiov;
     struct VirtIOBlockReq *next;
+    /* Members that need clearing, must be added prior to elem */
+    VirtQueueElement elem;
 } VirtIOBlockReq;