linux-kernel - Re: your mail

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Date:   Mon, 08 Apr 2019 13:04:03 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Fam Zheng <fam@...hon.net>, Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>, kvm@...r.kernel.org,
        Wolfram Sang <wsa@...-dreams.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Liang Cunming <cunming.liang@...el.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        "David S . Miller" <davem@...emloft.net>,
        Jens Axboe <axboe@...com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liu Changpeng <changpeng.liu@...el.com>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Amnon Ilan <ailan@...hat.com>, Christoph Hellwig <hch@....de>,
        John Ferlan <jferlan@...hat.com>
Subject: Re: your mail

On Tue, 2019-03-19 at 09:22 -0600, Keith Busch wrote:
> On Tue, Mar 19, 2019 at 04:41:07PM +0200, Maxim Levitsky wrote:
> >   -> Share the NVMe device between host and guest. 
> >      Even in fully virtualized configurations,
> >      some partitions of nvme device could be used by guests as block
> > devices 
> >      while others passed through with nvme-mdev to achieve balance between
> >      all features of full IO stack emulation and performance.
> >   
> >   -> NVME-MDEV is a bit faster due to the fact that in-kernel driver 
> >      can send interrupts to the guest directly without a context 
> >      switch that can be expensive due to meltdown mitigation.
> > 
> >   -> Is able to utilize interrupts to get reasonable performance. 
> >      This is only implemented
> >      as a proof of concept and not included in the patches, 
> >      but interrupt driven mode shows reasonable performance
> >      
> >   -> This is a framework that later can be used to support NVMe devices 
> >      with more of the IO virtualization built-in 
> >      (IOMMU with PASID support coupled with device that supports it)
> 
> Would be very interested to see the PASID support. You wouldn't even
> need to mediate the IO doorbells or translations if assigning entire
> namespaces, and should be much faster than the shadow doorbells.
> 
> I think you should send 6/9 "nvme/pci: init shadow doorbell after each
> reset" separately for immediate inclusion.
> 
> I like the idea in principle, but it will take me a little time to get
> through reviewing your implementation. I would have guessed we could
> have leveraged something from the existing nvme/target for the mediating
> controller register access and admin commands. Maybe even start with
> implementing an nvme passthrough namespace target type (we currently
> have block and file).


Hi!

Sorry to bother you, but any update?

I was somewhat sick for the last week, now finally back in shape to continue
working on this and other tasks I have.

I am studing now the nvme target code and the io_uring to evaluate the
difficultiy of using something similiar to talk to the block device instead of /
in addtion to the  direct connection I implemented.

I would be glad to hear more feedback on this project.

I will also soon post the few fixes separately as you suggested.

Best regards,
    Maxim Levitskky