linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Chao Peng <chao.p.peng@linux.intel.com>
Cc: Zha Bin <zhabin@linux.alibaba.com>,
	linux-kernel@vger.kernel.org, jasowang@redhat.com,
	slp@redhat.com, virtio-dev@lists.oasis-open.org,
	qemu-devel@nongnu.org, gerry@linux.alibaba.com,
	jing2.liu@linux.intel.com
Subject: Re: [PATCH v2 0/5] virtio mmio specification enhancement
Date: Tue, 11 Feb 2020 05:57:09 -0500	[thread overview]
Message-ID: <20200211053953-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20200211160541.GA37446@chaop.bj.intel.com>

On Tue, Feb 11, 2020 at 04:05:41PM +0000, Chao Peng wrote:
> On Mon, Feb 10, 2020 at 06:44:50AM -0500, Michael S. Tsirkin wrote:
> > 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?
> 
> Right, that is just a rough statistics.

Please try not to make them look so wrong then.
E.g. you don't include drivers/base/platform-msi.c for
mmio do you? Your patch brings a bunch of code in there.

> Surely enough, some drivers will
> never get enabled in a typcial config.
> 
> > Sure enough:
> > 
> > $ find drivers/pci -name '*c' |wc -l
> > 150
> 
> and plus:
> $ find arch/x86/pci/ -name '*c' |wc -l
> 22

But what's the point? This is code that is maintained by PCI core
people anyway.

> > 
> > 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.
> 
> Since current virtio-mmio size is small enough, so adding any notable
> feature would easily double it.

But really unlike PCI this is just PV stuff that is not reused by
anyone. We end up maintaining all this by ourselves.

> I have no objection that it may one day
> reach the same level of PCI, but in this patch some are actually
> generic changes and for MSI specific code we provide the option to
> confige away.
> 
> Thanks,
> Chao

The option will make it fall down at runtime but
it does not actually seem to remove all of the overhead.



> > 
> > 
> > -- 
> > MST


  reply	other threads:[~2020-02-11 10:57 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10  9:05 Zha Bin
2020-02-10  9:05 ` [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue Zha Bin
2020-02-11 10:50   ` Michael S. Tsirkin
2020-02-11 11:33   ` Michael S. Tsirkin
2020-02-12  3:39     ` Jason Wang
2020-02-12  8:18       ` Michael S. Tsirkin
2020-02-12  8:53         ` Jason Wang
2020-02-12  9:33           ` Jason Wang
2020-02-12  9:55             ` Michael S. Tsirkin
2020-02-13  3:38               ` Jason Wang
2020-02-10  9:05 ` [PATCH v2 2/5] virtio-mmio: refactor common functionality Zha Bin
2020-02-11 11:19   ` Michael S. Tsirkin
2020-02-12  2:58     ` [virtio-dev] " Liu, Jing2
2020-02-12  7:29       ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 3/5] virtio-mmio: create a generic MSI irq domain Zha Bin
2020-02-11 11:16   ` Michael S. Tsirkin
2020-02-12  7:40   ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support Zha Bin
2020-02-11  3:17   ` Jason Wang
2020-02-11  3:35     ` [virtio-dev] " Liu, Jing2
2020-02-11  4:02       ` Jason Wang
     [not found]         ` <5522f205-207b-b012-6631-3cc77dde3bfe@linux.intel.com>
2020-02-11  7:40           ` Jason Wang
2020-02-11 11:58             ` Michael S. Tsirkin
2020-02-11 12:04               ` Jason Wang
2020-02-11 12:08                 ` Michael S. Tsirkin
2020-02-11 12:18                   ` Jason Wang
2020-02-11 14:00                     ` Michael S. Tsirkin
2020-02-12  9:03                       ` Jason Wang
2020-02-12  9:15                         ` Michael S. Tsirkin
     [not found]             ` <4c19292f-9d25-a859-3dde-6dd5a03fdf0b@linux.intel.com>
2020-02-12  7:33               ` Michael S. Tsirkin
2020-02-12  9:06               ` Jason Wang
2020-02-12  9:16                 ` Michael S. Tsirkin
2020-02-13  3:40                   ` Jason Wang
2020-02-11 11:21       ` Michael S. Tsirkin
2020-02-11 11:11   ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 5/5] x86: virtio-mmio: support virtio-mmio with MSI for x86 Zha Bin
2020-02-11 11:14   ` Michael S. Tsirkin
2020-02-10 11:44 ` [PATCH v2 0/5] virtio mmio specification enhancement Michael S. Tsirkin
2020-02-11 16:05   ` Chao Peng
2020-02-11 10:57     ` Michael S. Tsirkin [this message]
     [not found] <DM6PR11MB4331B490586462DE7353E0B8F9710@DM6PR11MB4331.namprd11.prod.outlook.com>
2020-07-31 10:13 ` Stefan Hajnoczi
2020-07-31 15:44 ` Alex Bennée
2020-08-03 16:19   ` Alex Bennée
2020-08-03 23:31   ` Pincus, Josh

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200211053953-mutt-send-email-mst@kernel.org \
    --to=mst@redhat.com \
    --cc=chao.p.peng@linux.intel.com \
    --cc=gerry@linux.alibaba.com \
    --cc=jasowang@redhat.com \
    --cc=jing2.liu@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=qemu-devel@nongnu.org \
    --cc=slp@redhat.com \
    --cc=virtio-dev@lists.oasis-open.org \
    --cc=zhabin@linux.alibaba.com \
    --subject='Re: [PATCH v2 0/5] virtio mmio specification enhancement' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).