* [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
@ 2012-03-30 8:50 zwu.kernel
2012-03-30 10:29 ` Stefan Hajnoczi
0 siblings, 1 reply; 6+ messages in thread
From: zwu.kernel @ 2012-03-30 8:50 UTC (permalink / raw)
To: qemu-devel; +Cc: kwolf, wuzhy, stefanha
From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
block.c | 22 ++++++++++++++++++++++
1 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/block.c b/block.c
index 1fbf4dd..6de6f89 100644
--- a/block.c
+++ b/block.c
@@ -1477,6 +1477,17 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
qemu_iovec_init_external(&qiov, &iov, 1);
+ /**
+ * In sync call context, when the vcpu is blocked, this throttling timer
+ * will not fire; so the I/O throttling function has to be disabled here
+ * if it has been enabled.
+ */
+ if (bs->io_limits_enabled) {
+ fprintf(stderr, "Disabling I/O throttling on '%s' due "
+ "to synchronous I/O.\n", bdrv_get_device_name(bs));
+ bdrv_io_limits_disable(bs);
+ }
+
if (qemu_in_coroutine()) {
/* Fast-path if already in coroutine context */
bdrv_rw_co_entry(&rwco);
@@ -1983,10 +1994,21 @@ static int guess_disk_lchs(BlockDriverState *bs,
struct partition *p;
uint32_t nr_sects;
uint64_t nb_sectors;
+ bool enabled;
bdrv_get_geometry(bs, &nb_sectors);
+ /**
+ * The function will be invoked during startup not only in sync I/O mode,
+ * but also in async I/O mode. So the I/O throttling function has to
+ * be disabled temporarily here, not permanently.
+ * When all sync I/O drivers are converted to async I/O, it will be restored
+ * to the original state.
+ */
+ enabled = bs->io_limits_enabled;
+ bs->io_limits_enabled = false;
ret = bdrv_read(bs, 0, buf, 1);
+ bs->io_limits_enabled = enabled;
if (ret < 0)
return -1;
/* test msdos magic */
--
1.7.6
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
2012-03-30 8:50 [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api zwu.kernel
@ 2012-03-30 10:29 ` Stefan Hajnoczi
2012-03-31 12:07 ` Zhi Yong Wu
2012-03-31 12:09 ` Zhi Yong Wu
0 siblings, 2 replies; 6+ messages in thread
From: Stefan Hajnoczi @ 2012-03-30 10:29 UTC (permalink / raw)
To: zwu.kernel; +Cc: kwolf, wuzhy, qemu-devel, stefanha
On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote:
> + * When all sync I/O drivers are converted to async I/O, it will be restored
> + * to the original state.
The problem here is that guess_disk_lchs() uses bdrv_read(), not
whether device emulation uses sync or async I/O. Converting devices
to async I/O will not fix this.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
2012-03-30 10:29 ` Stefan Hajnoczi
@ 2012-03-31 12:07 ` Zhi Yong Wu
2012-04-02 7:31 ` Stefan Hajnoczi
2012-03-31 12:09 ` Zhi Yong Wu
1 sibling, 1 reply; 6+ messages in thread
From: Zhi Yong Wu @ 2012-03-31 12:07 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: kwolf, wuzhy, qemu-devel, stefanha
On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote:
>> + * When all sync I/O drivers are converted to async I/O, it will be restored
>> + * to the original state.
>
> The problem here is that guess_disk_lchs() uses bdrv_read(), not
> whether device emulation uses sync or async I/O. Converting devices
> to async I/O will not fix this.
Yeah, but when all sync emulated devices drivers are converted to
async mode, the code change need to be rolled back. This is what i
mean.
>
> Stefan
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
2012-03-31 12:07 ` Zhi Yong Wu
@ 2012-04-02 7:31 ` Stefan Hajnoczi
0 siblings, 0 replies; 6+ messages in thread
From: Stefan Hajnoczi @ 2012-04-02 7:31 UTC (permalink / raw)
To: Zhi Yong Wu; +Cc: kwolf, Stefan Hajnoczi, wuzhy, qemu-devel
On Sat, Mar 31, 2012 at 08:07:25PM +0800, Zhi Yong Wu wrote:
> On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote:
> >> + * When all sync I/O drivers are converted to async I/O, it will be restored
> >> + * to the original state.
> >
> > The problem here is that guess_disk_lchs() uses bdrv_read(), not
> > whether device emulation uses sync or async I/O. Converting devices
> > to async I/O will not fix this.
> Yeah, but when all sync emulated devices drivers are converted to
> async mode, the code change need to be rolled back. This is what i
> mean.
There are places outside device emulation that call bdrv_read(), like
guest_disk_lchs() and bdrv_commit(). We would need to convert them
before it's safe to remove the code to disable I/O throttling in
bdrv_read()/bdrv_write().
It's not okay to drop the code before all bdrv_read()/bdrv_write()
callers that are in a code path where I/O limits can be enabled have
been fixed (including guest_disk_lchs()) because a request that exceeds
I/O limits would cause QEMU to hang.
Once all devices have been converted it might be possible to temporarily
disable throttling in bdrv_read()/bdrv_write() and never disable it
permanently. This is because the bdrv_read()/bdrv_write() calls would
only come from QEMU code that is not directly driven by the guest - here
we probably don't need to apply I/O limits anyway. In other words,
devices use bdrv_aio_*() and I/O limits apply, QEMU internal code might
still use bdrv_read()/bdrv_write() and limits will not apply.
Anyway, I think it's best to drop this part of the comment because it's
more related to the disable code in bdrv_read()/bdrv_write() than to
this patch.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
2012-03-30 10:29 ` Stefan Hajnoczi
2012-03-31 12:07 ` Zhi Yong Wu
@ 2012-03-31 12:09 ` Zhi Yong Wu
2012-04-02 7:42 ` Stefan Hajnoczi
1 sibling, 1 reply; 6+ messages in thread
From: Zhi Yong Wu @ 2012-03-31 12:09 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: kwolf, wuzhy, qemu-devel, stefanha
On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote:
>> + * When all sync I/O drivers are converted to async I/O, it will be restored
>> + * to the original state.
>
> The problem here is that guess_disk_lchs() uses bdrv_read(), not
> whether device emulation uses sync or async I/O. Converting devices
> to async I/O will not fix this.
By the way, when you did testing, you applied #1 of this patchset? I
think that it make sense for that assert issue to be fixed.
>
> Stefan
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api
2012-03-31 12:09 ` Zhi Yong Wu
@ 2012-04-02 7:42 ` Stefan Hajnoczi
0 siblings, 0 replies; 6+ messages in thread
From: Stefan Hajnoczi @ 2012-04-02 7:42 UTC (permalink / raw)
To: Zhi Yong Wu; +Cc: kwolf, wuzhy, qemu-devel, stefanha
On Sat, Mar 31, 2012 at 08:09:46PM +0800, Zhi Yong Wu wrote:
> On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote:
> >> + * When all sync I/O drivers are converted to async I/O, it will be restored
> >> + * to the original state.
> >
> > The problem here is that guess_disk_lchs() uses bdrv_read(), not
> > whether device emulation uses sync or async I/O. Converting devices
> > to async I/O will not fix this.
> By the way, when you did testing, you applied #1 of this patchset? I
> think that it make sense for that assert issue to be fixed.
Yes, I applied both patches 1 and 2.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-04-02 8:27 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2012-03-30 8:50 [Qemu-devel] [PATCH v3 2/2] block: disable I/O throttling on sync api zwu.kernel
2012-03-30 10:29 ` Stefan Hajnoczi
2012-03-31 12:07 ` Zhi Yong Wu
2012-04-02 7:31 ` Stefan Hajnoczi
2012-03-31 12:09 ` Zhi Yong Wu
2012-04-02 7:42 ` Stefan Hajnoczi
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).