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From: Stefan Hajnoczi <stefanha@redhat.com>
To: Pankaj Gupta <pagupta@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	qemu-devel@nongnu.org, linux-nvdimm@ml01.01.org,
	linux-mm@kvack.org, kwolf@redhat.com,
	haozhong zhang <haozhong.zhang@intel.com>,
	jack@suse.cz, xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
	riel@surriel.com, niteshnarayanlal@hotmail.com, david@redhat.com,
	ross zwisler <ross.zwisler@intel.com>,
	lcapitulino@redhat.com, hch@infradead.org, mst@redhat.com,
	imammedo@redhat.com, marcel@redhat.com, pbonzini@redhat.com,
	dan j williams <dan.j.williams@intel.com>,
	nilal@redhat.com
Subject: Re: [Qemu-devel] [RFC v2 1/2] virtio: add pmem driver
Date: Fri, 27 Apr 2018 14:31:46 +0100	[thread overview]
Message-ID: <20180427133146.GB11150@stefanha-x1.localdomain> (raw)
In-Reply-To: <197910974.22984070.1524757499459.JavaMail.zimbra@redhat.com>

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On Thu, Apr 26, 2018 at 11:44:59AM -0400, Pankaj Gupta wrote:
> > > +	int err;
> > > +
> > > +	sg_init_one(&sg, buf, sizeof(buf));
> > > +
> > > +	err = virtqueue_add_outbuf(vpmem->req_vq, &sg, 1, buf, GFP_KERNEL);
> > > +
> > > +	if (err) {
> > > +		dev_err(&vdev->dev, "failed to send command to virtio pmem device\n");
> > > +		return;
> > > +	}
> > > +
> > > +	virtqueue_kick(vpmem->req_vq);
> > 
> > Is any locking necessary?  Two CPUs must not invoke virtio_pmem_flush()
> > at the same time.  Not sure if anything guarantees this, maybe you're
> > relying on libnvdimm but I haven't checked.
> 
> I thought about it to some extent, and wanted to go ahead with simple version first:
> 
> - I think file 'inode -> locking' sill is there for request on single file.
> - For multiple files, our aim is to just flush the backend block image.
> - Even there is collision for virt queue read/write entry it should just trigger a Qemu fsync. 
>   We just want most recent flush to assure guest writes are synced properly.
> 
> Important point here: We are doing entire block fsync for guest virtual disk.

I don't understand your answer.  Is locking necessary or not?

From the virtqueue_add_outbuf() documentation:

 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).

Stefan

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  reply	other threads:[~2018-04-27 13:32 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25 11:24 [RFC v2 0/2] kvm "fake DAX" device flushing Pankaj Gupta
2018-04-25 11:24 ` [RFC v2 1/2] virtio: add pmem driver Pankaj Gupta
2018-04-25 14:21   ` Dan Williams
2018-04-25 14:43     ` Dan Williams
2018-04-26 12:27       ` Jeff Moyer
2018-04-26 17:15         ` [Qemu-devel] " Pankaj Gupta
2018-04-26 17:24           ` Jeff Moyer
2018-04-25 14:52   ` Michael S. Tsirkin
2018-04-25 15:11     ` [Qemu-devel] " Pankaj Gupta
2018-04-26 13:12   ` Stefan Hajnoczi
2018-04-26 15:44     ` Pankaj Gupta
2018-04-27 13:31       ` Stefan Hajnoczi [this message]
2018-04-28 10:48         ` Pankaj Gupta
2018-04-25 11:24 ` [RFC v2 2/2] pmem: device flush over VIRTIO Pankaj Gupta
2018-04-25 14:23   ` Dan Williams
2018-04-25 14:47     ` Pankaj Gupta
2018-04-26 13:15   ` Stefan Hajnoczi
2018-04-26 16:40     ` Pankaj Gupta
2018-04-26 16:57       ` Dan Williams
2018-04-26 17:13         ` Pankaj Gupta
2018-04-25 11:24 ` [RFC v2] qemu: Add virtio pmem device Pankaj Gupta
2018-04-25 11:35   ` [Qemu-devel] " no-reply
2018-04-25 11:58     ` Pankaj Gupta
2018-04-25 14:23       ` Eric Blake
2018-04-25 14:51         ` Pankaj Gupta
2018-04-25 11:46   ` no-reply
2018-04-25 14:25   ` Eric Blake
2018-04-25 14:55     ` Pankaj Gupta
2018-04-26 13:24   ` Stefan Hajnoczi
2018-04-26 16:43     ` [Qemu-devel] " Pankaj Gupta
2018-06-01 12:24 ` [Qemu-devel] [RFC v2 0/2] kvm "fake DAX" device flushing Igor Mammedov
2018-06-04  5:56   ` Pankaj Gupta
2018-06-04  9:55   ` David Hildenbrand

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