linux-kernel - Re: vfio_pin_map_dma cause synchronize

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Message-ID: <561fb205-16be-ae87-9cfe-61e6a3b04dc5@huawei.com>
Date:   Mon, 2 Dec 2019 17:42:13 +0800
From:   "Longpeng (Mike)" <longpeng2@...wei.com>
To:     Paolo Bonzini <pbonzini@...hat.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

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( 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

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
> 
> 
> 


-- 
Regards,
Longpeng(Mike)