* [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
@ 2012-02-26 14:55 Stefan Hajnoczi
2012-02-27 7:35 ` Zhi Yong Wu
2012-02-27 14:20 ` Zhi Yong Wu
0 siblings, 2 replies; 9+ messages in thread
From: Stefan Hajnoczi @ 2012-02-26 14:55 UTC (permalink / raw)
To: qemu-devel; +Cc: Kevin Wolf, Stefan Hajnoczi, Zhi Yong Wu
The QED dirty bit timer marks the file clean after allocating writes
have drained. This is cheaper than clearing/setting the dirty bit on
each allocating write because the timer introduces a grace period which
can be extended if more allocating writes arrive.
The vm_clock was used in an attempt to prevent modifying the image file
when live migration has stopped the VM. Unfortunately vm_clock is
unavailable in the qemu-tool environment and will abort(3)!
Since QED currently does not support live migration, just replace
vm_clock with rt_clock and add comments explaining the migration
blocker.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
Zhi Yong: This patch is needed in addition to the qemu_init_main_loop() patches
you sent recently. Without this patch QED may read the vm_clock, which calls
abort(3) in qemu-tool.c. Together, our patches make QED work again in qemu-img
and qemu-io.
block/qed.c | 16 +++++++++++-----
1 files changed, 11 insertions(+), 5 deletions(-)
diff --git a/block/qed.c b/block/qed.c
index a041d31..fdb90e3 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -353,10 +353,7 @@ static void qed_start_need_check_timer(BDRVQEDState *s)
{
trace_qed_start_need_check_timer(s);
- /* Use vm_clock so we don't alter the image file while suspended for
- * migration.
- */
- qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(vm_clock) +
+ qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(rt_clock) +
get_ticks_per_sec() * QED_NEED_CHECK_TIMEOUT);
}
@@ -494,9 +491,18 @@ static int bdrv_qed_open(BlockDriverState *bs, int flags)
}
}
- s->need_check_timer = qemu_new_timer_ns(vm_clock,
+ s->need_check_timer = qemu_new_timer_ns(rt_clock,
qed_need_check_timer_cb, s);
+ /* There are two issues with live migration:
+ *
+ * 1. The destination will open the image file and see the dirty bit is
+ * set, causing it to "repair" the image while the source still has it
+ * open for writing.
+ *
+ * 2. The timer used for clearing the dirty bit uses rt_clock and can in
+ * theory fire when the VM is not running during migration.
+ */
error_set(&s->migration_blocker,
QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,
"qed", bs->device_name, "live migration");
--
1.7.9
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-26 14:55 [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility Stefan Hajnoczi
@ 2012-02-27 7:35 ` Zhi Yong Wu
2012-02-27 8:42 ` Paolo Bonzini
2012-02-27 14:20 ` Zhi Yong Wu
1 sibling, 1 reply; 9+ messages in thread
From: Zhi Yong Wu @ 2012-02-27 7:35 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: Kevin Wolf, qemu-devel, Zhi Yong Wu
On Sun, Feb 26, 2012 at 10:55 PM, Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> wrote:
> The QED dirty bit timer marks the file clean after allocating writes
> have drained. This is cheaper than clearing/setting the dirty bit on
> each allocating write because the timer introduces a grace period which
> can be extended if more allocating writes arrive.
>
> The vm_clock was used in an attempt to prevent modifying the image file
> when live migration has stopped the VM. Unfortunately vm_clock is
> unavailable in the qemu-tool environment and will abort(3)!
>
> Since QED currently does not support live migration, just replace
> vm_clock with rt_clock and add comments explaining the migration
> blocker.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
> Zhi Yong: This patch is needed in addition to the qemu_init_main_loop() patches
> you sent recently. Without this patch QED may read the vm_clock, which calls
> abort(3) in qemu-tool.c. Together, our patches make QED work again in qemu-img
Since vm_clock is created via qemu_init_main_loop(), when QED read
vm_clock, why will this call abort()?
Can you elaborate this? what is its call path?
> and qemu-io.
>
> block/qed.c | 16 +++++++++++-----
> 1 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/block/qed.c b/block/qed.c
> index a041d31..fdb90e3 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -353,10 +353,7 @@ static void qed_start_need_check_timer(BDRVQEDState *s)
> {
> trace_qed_start_need_check_timer(s);
>
> - /* Use vm_clock so we don't alter the image file while suspended for
> - * migration.
> - */
> - qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(vm_clock) +
> + qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(rt_clock) +
> get_ticks_per_sec() * QED_NEED_CHECK_TIMEOUT);
> }
>
> @@ -494,9 +491,18 @@ static int bdrv_qed_open(BlockDriverState *bs, int flags)
> }
> }
>
> - s->need_check_timer = qemu_new_timer_ns(vm_clock,
> + s->need_check_timer = qemu_new_timer_ns(rt_clock,
> qed_need_check_timer_cb, s);
>
> + /* There are two issues with live migration:
> + *
> + * 1. The destination will open the image file and see the dirty bit is
> + * set, causing it to "repair" the image while the source still has it
> + * open for writing.
> + *
> + * 2. The timer used for clearing the dirty bit uses rt_clock and can in
> + * theory fire when the VM is not running during migration.
> + */
> error_set(&s->migration_blocker,
> QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,
> "qed", bs->device_name, "live migration");
> --
> 1.7.9
>
>
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 7:35 ` Zhi Yong Wu
@ 2012-02-27 8:42 ` Paolo Bonzini
2012-02-27 8:48 ` Zhi Yong Wu
2012-02-27 9:31 ` Kevin Wolf
0 siblings, 2 replies; 9+ messages in thread
From: Paolo Bonzini @ 2012-02-27 8:42 UTC (permalink / raw)
To: Zhi Yong Wu; +Cc: Kevin Wolf, Zhi Yong Wu, Stefan Hajnoczi, qemu-devel
On 02/27/2012 08:35 AM, Zhi Yong Wu wrote:
> Since vm_clock is created via qemu_init_main_loop(), when QED read
> vm_clock, why will this call abort()?
> Can you elaborate this? what is its call path?
>
It will crash in cpu_get_clock() (in qemu-tool.c).
Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 8:42 ` Paolo Bonzini
@ 2012-02-27 8:48 ` Zhi Yong Wu
2012-02-27 9:31 ` Kevin Wolf
1 sibling, 0 replies; 9+ messages in thread
From: Zhi Yong Wu @ 2012-02-27 8:48 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Kevin Wolf, Zhi Yong Wu, Stefan Hajnoczi, qemu-devel
On Mon, Feb 27, 2012 at 4:42 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 02/27/2012 08:35 AM, Zhi Yong Wu wrote:
>> Since vm_clock is created via qemu_init_main_loop(), when QED read
>> vm_clock, why will this call abort()?
>> Can you elaborate this? what is its call path?
>>
>
> It will crash in cpu_get_clock() (in qemu-tool.c).
nice, got it. thanks.
>
> Paolo
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 8:42 ` Paolo Bonzini
2012-02-27 8:48 ` Zhi Yong Wu
@ 2012-02-27 9:31 ` Kevin Wolf
2012-02-27 11:14 ` Stefan Hajnoczi
1 sibling, 1 reply; 9+ messages in thread
From: Kevin Wolf @ 2012-02-27 9:31 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Zhi Yong Wu, Zhi Yong Wu, Stefan Hajnoczi, qemu-devel
Am 27.02.2012 09:42, schrieb Paolo Bonzini:
> On 02/27/2012 08:35 AM, Zhi Yong Wu wrote:
>> Since vm_clock is created via qemu_init_main_loop(), when QED read
>> vm_clock, why will this call abort()?
>> Can you elaborate this? what is its call path?
>>
>
> It will crash in cpu_get_clock() (in qemu-tool.c).
The fix isn't very nice if it makes migration impossible. I'd like to
introduce a similar timer in qcow2 which does support migration and
breaking it is not an option. So what about (completely untested)...
diff --git a/qemu-tool.c b/qemu-tool.c
index 183a583..edb84f5 100644
--- a/qemu-tool.c
+++ b/qemu-tool.c
@@ -61,7 +61,7 @@ void monitor_protocol_event(MonitorEvent event,
QObject *data)
int64_t cpu_get_clock(void)
{
- abort();
+ return 0;
}
int64_t cpu_get_icount(void)
Kevin
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 9:31 ` Kevin Wolf
@ 2012-02-27 11:14 ` Stefan Hajnoczi
0 siblings, 0 replies; 9+ messages in thread
From: Stefan Hajnoczi @ 2012-02-27 11:14 UTC (permalink / raw)
To: Kevin Wolf
Cc: Zhi Yong Wu, Paolo Bonzini, qemu-devel, Stefan Hajnoczi, Zhi Yong Wu
On Mon, Feb 27, 2012 at 9:31 AM, Kevin Wolf <kwolf@redhat.com> wrote:
> Am 27.02.2012 09:42, schrieb Paolo Bonzini:
>> On 02/27/2012 08:35 AM, Zhi Yong Wu wrote:
>>> Since vm_clock is created via qemu_init_main_loop(), when QED read
>>> vm_clock, why will this call abort()?
>>> Can you elaborate this? what is its call path?
>>>
>>
>> It will crash in cpu_get_clock() (in qemu-tool.c).
>
> The fix isn't very nice if it makes migration impossible. I'd like to
> introduce a similar timer in qcow2 which does support migration and
> breaking it is not an option. So what about (completely untested)...
>
> diff --git a/qemu-tool.c b/qemu-tool.c
> index 183a583..edb84f5 100644
> --- a/qemu-tool.c
> +++ b/qemu-tool.c
> @@ -61,7 +61,7 @@ void monitor_protocol_event(MonitorEvent event,
> QObject *data)
>
> int64_t cpu_get_clock(void)
> {
> - abort();
> + return 0;
> }
This is what we used to do, I'm okay with it.
Stefan
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-26 14:55 [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility Stefan Hajnoczi
2012-02-27 7:35 ` Zhi Yong Wu
@ 2012-02-27 14:20 ` Zhi Yong Wu
2012-02-27 14:41 ` Stefan Hajnoczi
1 sibling, 1 reply; 9+ messages in thread
From: Zhi Yong Wu @ 2012-02-27 14:20 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: Kevin Wolf, qemu-devel, Zhi Yong Wu
On Sun, Feb 26, 2012 at 10:55 PM, Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> wrote:
> The QED dirty bit timer marks the file clean after allocating writes
> have drained. This is cheaper than clearing/setting the dirty bit on
> each allocating write because the timer introduces a grace period which
> can be extended if more allocating writes arrive.
>
> The vm_clock was used in an attempt to prevent modifying the image file
Why can vm_clock do this work but other clock can not? If you're
available, can you elaborate what the difference among the three
clocks is? such as vm_clock, rt_clock, and host_clock.
> when live migration has stopped the VM. Unfortunately vm_clock is
> unavailable in the qemu-tool environment and will abort(3)!
>
> Since QED currently does not support live migration, just replace
> vm_clock with rt_clock and add comments explaining the migration
> blocker.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
> Zhi Yong: This patch is needed in addition to the qemu_init_main_loop() patches
> you sent recently. Without this patch QED may read the vm_clock, which calls
> abort(3) in qemu-tool.c. Together, our patches make QED work again in qemu-img
> and qemu-io.
>
> block/qed.c | 16 +++++++++++-----
> 1 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/block/qed.c b/block/qed.c
> index a041d31..fdb90e3 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -353,10 +353,7 @@ static void qed_start_need_check_timer(BDRVQEDState *s)
> {
> trace_qed_start_need_check_timer(s);
>
> - /* Use vm_clock so we don't alter the image file while suspended for
> - * migration.
> - */
> - qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(vm_clock) +
> + qemu_mod_timer(s->need_check_timer, qemu_get_clock_ns(rt_clock) +
> get_ticks_per_sec() * QED_NEED_CHECK_TIMEOUT);
> }
>
> @@ -494,9 +491,18 @@ static int bdrv_qed_open(BlockDriverState *bs, int flags)
> }
> }
>
> - s->need_check_timer = qemu_new_timer_ns(vm_clock,
> + s->need_check_timer = qemu_new_timer_ns(rt_clock,
> qed_need_check_timer_cb, s);
>
> + /* There are two issues with live migration:
> + *
> + * 1. The destination will open the image file and see the dirty bit is
> + * set, causing it to "repair" the image while the source still has it
> + * open for writing.
> + *
> + * 2. The timer used for clearing the dirty bit uses rt_clock and can in
> + * theory fire when the VM is not running during migration.
> + */
> error_set(&s->migration_blocker,
> QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,
> "qed", bs->device_name, "live migration");
> --
> 1.7.9
>
>
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 14:20 ` Zhi Yong Wu
@ 2012-02-27 14:41 ` Stefan Hajnoczi
2012-02-27 15:17 ` Zhi Yong Wu
0 siblings, 1 reply; 9+ messages in thread
From: Stefan Hajnoczi @ 2012-02-27 14:41 UTC (permalink / raw)
To: Zhi Yong Wu; +Cc: Kevin Wolf, Zhi Yong Wu, Stefan Hajnoczi, qemu-devel
On Mon, Feb 27, 2012 at 2:20 PM, Zhi Yong Wu <zwu.kernel@gmail.com> wrote:
> On Sun, Feb 26, 2012 at 10:55 PM, Stefan Hajnoczi
> <stefanha@linux.vnet.ibm.com> wrote:
>> The QED dirty bit timer marks the file clean after allocating writes
>> have drained. This is cheaper than clearing/setting the dirty bit on
>> each allocating write because the timer introduces a grace period which
>> can be extended if more allocating writes arrive.
>>
>> The vm_clock was used in an attempt to prevent modifying the image file
> Why can vm_clock do this work but other clock can not? If you're
> available, can you elaborate what the difference among the three
> clocks is? such as vm_clock, rt_clock, and host_clock.
See qemu-timer.h.
Stefan
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility
2012-02-27 14:41 ` Stefan Hajnoczi
@ 2012-02-27 15:17 ` Zhi Yong Wu
0 siblings, 0 replies; 9+ messages in thread
From: Zhi Yong Wu @ 2012-02-27 15:17 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: Kevin Wolf, Zhi Yong Wu, Stefan Hajnoczi, qemu-devel
On Mon, Feb 27, 2012 at 10:41 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Mon, Feb 27, 2012 at 2:20 PM, Zhi Yong Wu <zwu.kernel@gmail.com> wrote:
>> On Sun, Feb 26, 2012 at 10:55 PM, Stefan Hajnoczi
>> <stefanha@linux.vnet.ibm.com> wrote:
>>> The QED dirty bit timer marks the file clean after allocating writes
>>> have drained. This is cheaper than clearing/setting the dirty bit on
>>> each allocating write because the timer introduces a grace period which
>>> can be extended if more allocating writes arrive.
>>>
>>> The vm_clock was used in an attempt to prevent modifying the image file
>> Why can vm_clock do this work but other clock can not? If you're
>> available, can you elaborate what the difference among the three
>> clocks is? such as vm_clock, rt_clock, and host_clock.
>
> See qemu-timer.h.
thanks
>
> Stefan
--
Regards,
Zhi Yong Wu
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2012-02-27 15:17 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-02-26 14:55 [Qemu-devel] [PATCH] qed: replace vm_clock with rt_clock for qemu-tool compatibility Stefan Hajnoczi
2012-02-27 7:35 ` Zhi Yong Wu
2012-02-27 8:42 ` Paolo Bonzini
2012-02-27 8:48 ` Zhi Yong Wu
2012-02-27 9:31 ` Kevin Wolf
2012-02-27 11:14 ` Stefan Hajnoczi
2012-02-27 14:20 ` Zhi Yong Wu
2012-02-27 14:41 ` Stefan Hajnoczi
2012-02-27 15:17 ` Zhi Yong Wu
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