* [Qemu-devel] qemu vs. kvm: When to flush the coalesced mmio buffer?
@ 2011-01-03 12:11 Jan Kiszka
2011-01-03 12:25 ` Gleb Natapov
2011-01-03 12:32 ` [Qemu-devel] " Avi Kivity
0 siblings, 2 replies; 4+ messages in thread
From: Jan Kiszka @ 2011-01-03 12:11 UTC (permalink / raw)
To: kvm, qemu-devel
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Hi again,
another subtle difference between qemu-kvm and upstream:
When we leave the guest for an IO window (KVM_RUN returns EINTR or
EAGAIN), we call kvm_flush_coalesced_mmio_buffer in qemu-kvm but not in
upstream. When version is better? I can't find any rationales in both
git logs.
Jan
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] qemu vs. kvm: When to flush the coalesced mmio buffer?
2011-01-03 12:11 [Qemu-devel] qemu vs. kvm: When to flush the coalesced mmio buffer? Jan Kiszka
@ 2011-01-03 12:25 ` Gleb Natapov
2011-01-03 12:32 ` [Qemu-devel] " Avi Kivity
1 sibling, 0 replies; 4+ messages in thread
From: Gleb Natapov @ 2011-01-03 12:25 UTC (permalink / raw)
To: Jan Kiszka; +Cc: qemu-devel, kvm
On Mon, Jan 03, 2011 at 01:11:32PM +0100, Jan Kiszka wrote:
> Hi again,
>
> another subtle difference between qemu-kvm and upstream:
>
> When we leave the guest for an IO window (KVM_RUN returns EINTR or
> EAGAIN), we call kvm_flush_coalesced_mmio_buffer in qemu-kvm but not in
> upstream. When version is better? I can't find any rationales in both
> git logs.
>
Since coalesced mmio is used to prevent unnecessary exits to userspace
if vcpu thread is already in userspace why not flush coalesced mmio
buffer?
--
Gleb.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Qemu-devel] Re: qemu vs. kvm: When to flush the coalesced mmio buffer?
2011-01-03 12:11 [Qemu-devel] qemu vs. kvm: When to flush the coalesced mmio buffer? Jan Kiszka
2011-01-03 12:25 ` Gleb Natapov
@ 2011-01-03 12:32 ` Avi Kivity
2011-01-03 12:34 ` Jan Kiszka
1 sibling, 1 reply; 4+ messages in thread
From: Avi Kivity @ 2011-01-03 12:32 UTC (permalink / raw)
To: Jan Kiszka; +Cc: qemu-devel, kvm
On 01/03/2011 02:11 PM, Jan Kiszka wrote:
> Hi again,
>
> another subtle difference between qemu-kvm and upstream:
>
> When we leave the guest for an IO window (KVM_RUN returns EINTR or
> EAGAIN), we call kvm_flush_coalesced_mmio_buffer in qemu-kvm but not in
> upstream. When version is better? I can't find any rationales in both
> git logs.
We must flush on EINTR, otherwise a live migration can leave some mmios
in the source host and not replay them on the destination host.
(plus, as Gleb says, if you're in userspace you might as well flush)
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Qemu-devel] Re: qemu vs. kvm: When to flush the coalesced mmio buffer?
2011-01-03 12:32 ` [Qemu-devel] " Avi Kivity
@ 2011-01-03 12:34 ` Jan Kiszka
0 siblings, 0 replies; 4+ messages in thread
From: Jan Kiszka @ 2011-01-03 12:34 UTC (permalink / raw)
To: Avi Kivity; +Cc: qemu-devel, kvm
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Am 03.01.2011 13:32, Avi Kivity wrote:
> On 01/03/2011 02:11 PM, Jan Kiszka wrote:
>> Hi again,
>>
>> another subtle difference between qemu-kvm and upstream:
>>
>> When we leave the guest for an IO window (KVM_RUN returns EINTR or
>> EAGAIN), we call kvm_flush_coalesced_mmio_buffer in qemu-kvm but not in
>> upstream. When version is better? I can't find any rationales in both
>> git logs.
>
> We must flush on EINTR, otherwise a live migration can leave some mmios
> in the source host and not replay them on the destination host.
>
> (plus, as Gleb says, if you're in userspace you might as well flush)
>
OK, will append a fix to my series.
Thanks,
Jan
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2011-01-03 12:11 [Qemu-devel] qemu vs. kvm: When to flush the coalesced mmio buffer? Jan Kiszka
2011-01-03 12:25 ` Gleb Natapov
2011-01-03 12:32 ` [Qemu-devel] " Avi Kivity
2011-01-03 12:34 ` Jan Kiszka
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