linux-kernel - Re: [PATCH v2 0/5] virtio mmio specification enhancement

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Date:   Mon, 10 Feb 2020 06:44:50 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Zha Bin <zhabin@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, jasowang@...hat.com, slp@...hat.com,
        virtio-dev@...ts.oasis-open.org, qemu-devel@...gnu.org,
        gerry@...ux.alibaba.com, jing2.liu@...ux.intel.com,
        chao.p.peng@...ux.intel.com
Subject: Re: [PATCH v2 0/5] virtio mmio specification enhancement

On Mon, Feb 10, 2020 at 05:05:16PM +0800, Zha Bin wrote:
> We have compared the number of files and the lines of code between
> virtio-mmio and virio-pci.
> 
> 				Virtio-PCI	    Virtio-MMIO	
> 	number of files(Linux)	    161			1
> 	lines of code(Linux)	    78237		538



Something's very wrong here. virtio PCI is 161 files?
Are you counting the whole PCI subsystem?
Sure enough:

$ find drivers/pci -name '*c' |wc -l
150

That's not reasonable, this includes a bunch of drivers that
never run on a typical hypervisor.

MMIO is also not as small as you are trying to show:

$ cloc drivers/virtio/virtio_mmio.c include/uapi/linux/virtio_mmio.h
       2 text files.
       2 unique files.                              
       0 files ignored.

github.com/AlDanial/cloc v 1.82  T=0.01 s (230.7 files/s, 106126.5 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                                1            144            100            535
C/C++ Header                     1             39             66             36
-------------------------------------------------------------------------------
SUM:                             2            183            166            571
-------------------------------------------------------------------------------


I don't doubt MMIO is smaller than PCI. Of course that's because it has
no features to speak of - just this patch already doubles it's size. If
we keep doing that because we want the features then they will reach
the same size in about 4 iterations.


-- 
MST