linux-kernel - Re: vfio_pin_map_dma cause synchronize

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Date:   Mon, 2 Dec 2019 10:31:11 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Longpeng (Mike)" <longpeng2@...wei.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     qemu-devel@...gnu.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Longpeng(Mike)" <longpeng.mike@...il.com>,
        Gonglei <arei.gonglei@...wei.com>,
        Huangzhichao <huangzhichao@...wei.com>
Subject: Re: vfio_pin_map_dma cause synchronize_sched wait too long

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( QEMU
> 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
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.

Paolo