qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCHv7 10/17] block: honour BlockLimits in bdrv_co_di


From: Peter Lieven
Subject: Re: [Qemu-devel] [PATCHv7 10/17] block: honour BlockLimits in bdrv_co_discard
Date: Tue, 12 Nov 2013 09:53:03 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0

On 11.11.2013 14:20, Kevin Wolf wrote:
Am 24.10.2013 um 12:06 hat Peter Lieven geschrieben:
Reviewed-by: Eric Blake <address@hidden>
Signed-off-by: Peter Lieven <address@hidden>
---
  block.c |   37 ++++++++++++++++++++++++++++++++++++-
  1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 0c0b0ac..b28dd42 100644
--- a/block.c
+++ b/block.c
@@ -4234,6 +4234,11 @@ static void coroutine_fn bdrv_discard_co_entry(void 
*opaque)
      rwco->ret = bdrv_co_discard(rwco->bs, rwco->sector_num, rwco->nb_sectors);
  }
+/* if no limit is specified in the BlockLimits use a default
+ * of 32768 512-byte sectors (16 MiB) per request.
+ */
+#define MAX_DISCARD_DEFAULT 32768
+
  int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
                                   int nb_sectors)
  {
@@ -4255,7 +4260,37 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, 
int64_t sector_num,
      }
if (bs->drv->bdrv_co_discard) {
-        return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
+        int max_discard = bs->bl.max_discard ?
+                          bs->bl.max_discard : MAX_DISCARD_DEFAULT;
+
+        while (nb_sectors > 0) {
+            int ret;
+            int num = nb_sectors;
+
+            /* align request */
+            if (bs->bl.discard_alignment &&
+                num >= bs->bl.discard_alignment &&
+                sector_num % bs->bl.discard_alignment) {
+                if (num > bs->bl.discard_alignment) {
+                    num = bs->bl.discard_alignment;
+                }
+                num -= sector_num % bs->bl.discard_alignment;
+            }
+
+            /* limit request size */
+            if (num > max_discard) {
+                num = max_discard;
+            }
+
+            ret = bs->drv->bdrv_co_discard(bs, sector_num, num);
+            if (ret) {
+                return ret;
+            }
+
+            sector_num += num;
+            nb_sectors -= num;
+        }
+        return 0;
      } else if (bs->drv->bdrv_aio_discard) {
          BlockDriverAIOCB *acb;
          CoroutineIOCompletion co = {
You're only optimising drivers which have a .bdrv_co_discard()
implementation, but not those with .bdrv_aio_discard(). Not very nice,
and it would have been easy to avoid this by putting the loop around the
whole if statement instead of inside the 'then' branch.
Good point. I wonder noone noticed before ;-)

Do you want me to respin or is ok to send a follow up patch?
Stefan has it already in block-next. This patch doesn't make
the situation worse and we need follow up patches for
all the drivers to supply alignment information anyway.

Peter




reply via email to

[Prev in Thread] Current Thread [Next in Thread]