I've made a mistake on the series. Following is the new patch:
>From ef1079b422eef40a802ca13e249795005efa441d Mon Sep 17 00:00:00 2001
From: Qingshu Chen <1150163...@qq.com>
Date: Tue, 21 Jul 2015 09:46:08 +0800
Subject: [PATCH] ignore bdrv_flush operation when no qcow2 cache item is
dirty
Signed-off-by: Qingshu Chen <qingshu.chen...@gmail.com>
---
block/qcow2-cache.c | 16 ++++++++++++----
block/qcow2.c | 2 ++
2 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 53b8afc..08d1884 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -174,23 +174,31 @@ int qcow2_cache_flush(BlockDriverState *bs,
Qcow2Cache *c)
int result = 0;
int ret;
int i;
+ bool flag = false;
trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache);
for (i = 0; i < c->size; i++) {
- ret = qcow2_cache_entry_flush(bs, c, i);
- if (ret < 0 && result != -ENOSPC) {
- result = ret;
+ if (c->entries[i].dirty && c->entries[i].offset) {
+ flag = true;
+ ret = qcow2_cache_entry_flush(bs, c, i);
+ if (ret < 0 && result != -ENOSPC) {
+ result = ret;
+ }
}
}
- if (result == 0) {
+ if (result == 0 && flag) {
ret = bdrv_flush(bs->file);
if (ret < 0) {
result = ret;
}
}
+ if (!flag && result >= 0) {
+ result = 1;
+ }
+
return result;
}
diff --git a/block/qcow2.c b/block/qcow2.c
index 76c331b..2e95cc1 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2505,6 +2505,8 @@ static coroutine_fn int
qcow2_co_flush_to_os(BlockDriverState *bs)
if (ret < 0) {
qemu_co_mutex_unlock(&s->lock);
return ret;
+ } else if (ret == 1) {
+ bdrv_flush(bs->file);
}
if (qcow2_need_accurate_refcounts(s)) {
--
1.9.1
2015-07-20 23:03 GMT+08:00 Eric Blake <ebl...@redhat.com>:
>
> [patches should always be sent to qemu-devel, even if qemu-block is also
> in the to/cc list]
>
> On 07/08/2015 01:26 AM, Qingshu Chen wrote:
> > qcow2_cache_flush() writes dirty cache to the disk and invokes
bdrv_flush()
> > to make the data durable. But even if there is no dirty cache,
> > qcow2_cache_flush() would invoke bdrv_flush(). In fact, bdrv_flush()
will
> > invoke fdatasync(), and it is an expensive operation. The patch will not
> > invoke bdrv_flush if there is not dirty cache. The reason that I modify
the
> > return value of qcow2_cache_flush() is qcow2_co_flush_to_os needs to
know
> > whether flush operation is called. Following is the patch:
> >
> >>From 23f9f83da4178e8fbb53d2cffe128f5a2d3a239a Mon Sep 17 00:00:00 2001
> > From: Qingshu Chen <qingshu.chen...@gmail.com>
> > Date: Wed, 1 Jul 2015 14:45:23 +0800
> > Subject: [PATCH 1/2] ignore bdrv_flush operation when no qcow2 cache
item is
> > dirty
> > Signed-off-by: Qingshu Chen <qingshu.chen...@gmail.com>
>
> I didn't quickly find an associated 2/2 patch; are you sure you sent the
> series correctly?
>
> >
> > ---
> > block/qcow2-cache.c | 9 ++++++++-
> > block/qcow2.c | 2 ++
> > 2 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
> > index ed92a09..57c0601 100644
> > --- a/block/qcow2-cache.c
> > +++ b/block/qcow2-cache.c
> > @@ -174,6 +174,7 @@ int qcow2_cache_flush(BlockDriverState *bs,
Qcow2Cache
> > *c)
> > int result = 0;
> > int ret;
> > int i;
> > + int flag = 0;
>
> This is used as a bool, so declare it as such (bool flag = false;).
>
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
--
-------------------------------------------------------------------------------------------------------------
Qingshu Chen,
Institute of Parallel and Distributed Systems (IPADS),
School of Software,
Shanghai Jiao Tong University
---------------------------------------------------------------------------------------------------------------
