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Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value f
From: |
Li, Liang Z |
Subject: |
Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation |
Date: |
Fri, 14 Aug 2015 01:23:25 +0000 |
> On Thu, Aug 13, 2015 at 01:25:29AM +0000, Li, Liang Z wrote:
> > Hi Paolo & Marcelo,
> >
> > Could please point out what issue the patch 317b0a6d8ba44e try to fix?
> > I
> found in live migration the cpu_synchronize_all_states will be called twice,
> and it will take more than 1 ms sometimes. I try to do some optimization but
> lack the knowledge about the background.
>
> What the code in 317b0a6d8ba44e requires is to retrieve the TSC value from
> the kernel.
I know 317b0a6d8ba44e is to retrieve the TSC value, but I don't understand why
it is needed. During the live migration, the cpu_synchronize_all_states will be
called later after stopping kvm-clock. The env->tsc will be updated, is that
not enough? Or is there some case like call the 'stop_vm(RUN_STATE_PAUSED )' or
' 'stop_vm (RUN_STATE_DEBUG) ', that require updating the env->tsc? By google,
I find that your patch try to fix some issue, but I don't know what the exact
issue.
Anyway, using cpu_synchronize_all_states to update the env->tsc is a littler
expensive, especially in the stop can copy stage.
Liang
> Perhaps you can trace kvm_arch_get_regs and look why its taking that
> amount of time and what can be done to improve it.
- [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Li, Liang Z, 2015/08/12
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Marcelo Tosatti, 2015/08/13
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation,
Li, Liang Z <=
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Marcin Gibuła, 2015/08/14
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Li, Liang Z, 2015/08/14
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Marcin Gibuła, 2015/08/14
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Li, Liang Z, 2015/08/14
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Marcin Gibuła, 2015/08/14
- Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation, Marcelo Tosatti, 2015/08/14