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Re: vfio_pin_map_dma cause synchronize_sched wait too long

From: Longpeng (Mike)
Subject: Re: vfio_pin_map_dma cause synchronize_sched wait too long
Date: Mon, 2 Dec 2019 17:42:13 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2

在 2019/12/2 17:31, Paolo Bonzini 写道:
> On 02/12/19 10:10, Longpeng (Mike) wrote:
>> Suppose there're two VMs: VM1 is bind to node-0 and calling 
>> vfio_pin_map_dma(),
>> VM2 is a migrate incoming VM which bind to node-1. We found the vm_start( 
>> function) of VM2 will take too long occasionally, the reason is as follow.
> Which part of vfio_pin_map_dma is running?  There is already a

I need more analysis to find which part.

> cond_resched in vfio_iommu_map.  Perhaps you could add one to
> vfio_pin_pages_remote and/or use vfio_pgsize_bitmap to cap the number of
> pages that it returns.

Um ... There's only one running task (qemu-kvm of the VM1) on that CPU, so maybe
the cond_resched() is ineffective ?

> > Paolo


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