Xen devel - Feb 2008 - [PATCH] stubdom: optimize block io completion polling

stubdom: optimize block io completion polling
by not polling all the time but just when some requests have completed.

Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>

diff -r c9122280dd86 extras/mini-os/blkfront.c
--- a/extras/mini-os/blkfront.c	Wed Feb 13 12:13:42 2008 +0000
+++ b/extras/mini-os/blkfront.c	Wed Feb 13 13:56:48 2008 +0000
@@ -370,6 +370,10 @@ moretodo:
     RING_FINAL_CHECK_FOR_RESPONSES(&dev->ring, more);
     if (more) goto moretodo;
 
+#ifdef HAVE_LIBC
+    if (!nr_consumed)
+        files[dev->fd].read = 0;
+#endif
     return nr_consumed;
 }
 
diff -r c9122280dd86 tools/ioemu/block-vbd.c
--- a/tools/ioemu/block-vbd.c	Wed Feb 13 12:13:42 2008 +0000
+++ b/tools/ioemu/block-vbd.c	Wed Feb 13 13:56:48 2008 +0000
@@ -67,6 +67,12 @@ static int vbd_probe(const uint8_t *buf,
     return 100;
 }
 
+static void vbd_io_completed(void *opaque)
+{
+    BDRVVbdState *s = opaque;
+    blkfront_aio_poll(s->dev);
+}
+
 static int vbd_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVVbdState *s = bs->opaque;
@@ -85,6 +91,7 @@ static int vbd_open(BlockDriverState *bs
     }
 
     s->fd = blkfront_open(s->dev);
+    qemu_set_fd_handler(s->fd, vbd_io_completed, NULL, s);
 
     QEMU_LIST_INSERT_HEAD(&vbds, s, list);
 
@@ -102,9 +109,6 @@ void qemu_aio_init(void)
 
 void qemu_aio_poll(void)
 {
-    BDRVVbdState *s;
-    for (s = vbds.lh_first; s; s = s->list.le_next)
-	blkfront_aio_poll(s->dev);
 }
 
 /* Wait for all IO requests to complete.  */

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Samuel Thibault, le Wed 13 Feb 2008 13:59:59 +0000, a écrit
:
> stubdom: optimize block io completion polling
> by not polling all the time but just when some requests have completed.
Oops, sorry, although it never happened during my tests, I''m pretty
sure
there is a race, please use this patch instead:

stubdom: optimize block io completion polling
by not polling all the time but just when some requests have completed.

Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>

diff -r e85399173769 extras/mini-os/blkfront.c
--- a/extras/mini-os/blkfront.c	Tue Feb 12 16:59:08 2008 +0000
+++ b/extras/mini-os/blkfront.c	Wed Feb 13 15:55:47 2008 +0000
@@ -327,6 +327,11 @@
     struct blkif_response *rsp;
 
 moretodo:
+#ifdef HAVE_LIBC
+    files[dev->fd].read = 0;
+    mb(); /* Make sure to let the handler set read to 1 before we start looking
at the ring */
+#endif
+
     rp = dev->ring.sring->rsp_prod;
     rmb(); /* Ensure we see queued responses up to ''rp''. */
     cons = dev->ring.rsp_cons;
--- a/tools/ioemu/block-vbd.c	Tue Feb 12 16:59:08 2008 +0000
+++ b/tools/ioemu/block-vbd.c	Wed Feb 13 15:55:47 2008 +0000
@@ -67,6 +67,12 @@
     return 100;
 }
 
+static void vbd_io_completed(void *opaque)
+{
+    BDRVVbdState *s = opaque;
+    blkfront_aio_poll(s->dev);
+}
+
 static int vbd_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVVbdState *s = bs->opaque;
@@ -85,6 +91,7 @@
     }
 
     s->fd = blkfront_open(s->dev);
+    qemu_set_fd_handler(s->fd, vbd_io_completed, NULL, s);
 
     QEMU_LIST_INSERT_HEAD(&vbds, s, list);
 
@@ -102,9 +109,6 @@
 
 void qemu_aio_poll(void)
 {
-    BDRVVbdState *s;
-    for (s = vbds.lh_first; s; s = s->list.le_next)
-	blkfront_aio_poll(s->dev);
 }
 
 /* Wait for all IO requests to complete.  */

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