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Re: [Qemu-devel] [v2 RESEND 0/4] Fix long vm downtime during live migrat
From: |
Amit Shah |
Subject: |
Re: [Qemu-devel] [v2 RESEND 0/4] Fix long vm downtime during live migration |
Date: |
Tue, 3 Nov 2015 17:53:06 +0530 |
On (Mon) 02 Nov 2015 [15:36:59], Liang Li wrote:
> The patch 3ea3b7fa9af067982f34b of kvm introduces a lazy collapsing
> of small sptes into large sptes mechanism, which intend to solve the
> performance drop issue if live migration fails or is canceled. The
> rmap will be scanned in the KVM_SET_USER_MEMORY_REGION ioctl context
> when dirty logging is stopped so as to drop the small sptes, scanning
> the rmap and drop the small sptes is a time consuming operation which
> will take dozens of milliseconds, the actual time depends on VM's
> memory size. For a VM with 8GB RAM, it will take about 30ms.
>
> The current QEMU code stop the dirty logging during the pause and
> copy stage by calling the migration_end() function. Now migration_end()
> is a time consuming operation because it calls
> memroy_global_dirty_log_stop(), which will trigger the scanning of rmap
> and dropping small sptes operation. So call migration_end() before all
> the vmsate data has already been transferred to the destination will
> prolong VM downtime.
>
> migration_end() should be deferred after all the data has been
> transferred to the destination. blk_mig_cleanup() can be deferred too.
Reviewed-by: Amit Shah <address@hidden>
Thanks for adding to the commit message, that helped.
Amit
- Re: [Qemu-devel] [v2 RESEND 1/4] migration: defer migration_end & blk_mig_cleanup, (continued)
- [Qemu-devel] [v2 RESEND 2/4] migration: rename qemu_savevm_state_cancel, Liang Li, 2015/11/02
- [Qemu-devel] [v2 RESEND 4/4] migration: code clean up, Liang Li, 2015/11/02
- [Qemu-devel] [v2 RESEND 3/4] migration: rename cancel to cleanup in SaveVMHandles, Liang Li, 2015/11/02
- Re: [Qemu-devel] [v2 RESEND 0/4] Fix long vm downtime during live migration, Paolo Bonzini, 2015/11/02
- Re: [Qemu-devel] [v2 RESEND 0/4] Fix long vm downtime during live migration, Stefan Hajnoczi, 2015/11/02
- Re: [Qemu-devel] [v2 RESEND 0/4] Fix long vm downtime during live migration,
Amit Shah <=