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Re: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate process

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  Re: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2017-01-17 20:30 +0100
    RE: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2017-01-18 06:10 +0100
      Re: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2017-01-18 16:40 +0100
        RE: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2017-01-19 02:50 +0100
          Re: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2017-01-20 17:40 +0100

#1560954 — Re: [PATCH v6 kernel 3/5] virtio-balloon: speed up inflate/deflate process

On Wed, Dec 21, 2016 at 02:52:26PM +0800, Liang Li wrote:
>  
> -	/* We should always be able to add one buffer to an empty queue. */
> -	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> -	virtqueue_kick(vq);
> +static void do_set_resp_bitmap(struct virtio_balloon *vb,
> +		unsigned long base_pfn, int pages)
>  
> -	/* When host has read buffer, this completes via balloon_ack */
> -	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> +{
> +	__le64 *range = vb->resp_data + vb->resp_pos;
>  
> +	if (pages > (1 << VIRTIO_BALLOON_NR_PFN_BITS)) {
> +		/* when the length field can't contain pages, set it to 0 to

/*
 * Multi-line
 * comments
 * should look like this.
 */

Also, pls start sentences with an upper-case letter.

> +		 * indicate the actual length is in the next __le64;
> +		 */

This is part of the interface so should be documented as such.

> +		*range = cpu_to_le64((base_pfn <<
> +				VIRTIO_BALLOON_NR_PFN_BITS) | 0);
> +		*(range + 1) = cpu_to_le64(pages);
> +		vb->resp_pos += 2;

Pls use structs for this kind of stuff.

> +	} else {
> +		*range = (base_pfn << VIRTIO_BALLOON_NR_PFN_BITS) | pages;
> +		vb->resp_pos++;
> +	}
> +}

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#1561272

> > -	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> > -	virtqueue_kick(vq);
> > +static void do_set_resp_bitmap(struct virtio_balloon *vb,
> > +		unsigned long base_pfn, int pages)
> >
> > -	/* When host has read buffer, this completes via balloon_ack */
> > -	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> > +{
> > +	__le64 *range = vb->resp_data + vb->resp_pos;
> >
> > +	if (pages > (1 << VIRTIO_BALLOON_NR_PFN_BITS)) {
> > +		/* when the length field can't contain pages, set it to 0 to
> 
> /*
>  * Multi-line
>  * comments
>  * should look like this.
>  */
> 
> Also, pls start sentences with an upper-case letter.
> 

Sorry for that.

> > +		 * indicate the actual length is in the next __le64;
> > +		 */
> 
> This is part of the interface so should be documented as such.
> 
> > +		*range = cpu_to_le64((base_pfn <<
> > +				VIRTIO_BALLOON_NR_PFN_BITS) | 0);
> > +		*(range + 1) = cpu_to_le64(pages);
> > +		vb->resp_pos += 2;
> 
> Pls use structs for this kind of stuff.

I am not sure if you mean to use 

struct  range {
 	__le64 pfn: 52;
	__le64 nr_page: 12
}
Instead of the shift operation?

I didn't use this way because I don't want to include 'virtio-balloon.h' in page_alloc.c,
or copy the define of this struct in page_alloc.c

Thanks!
Liang

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#1561901

On Wed, Jan 18, 2017 at 04:56:58AM +0000, Li, Liang Z wrote:
> > > -	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> > > -	virtqueue_kick(vq);
> > > +static void do_set_resp_bitmap(struct virtio_balloon *vb,
> > > +		unsigned long base_pfn, int pages)
> > >
> > > -	/* When host has read buffer, this completes via balloon_ack */
> > > -	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> > > +{
> > > +	__le64 *range = vb->resp_data + vb->resp_pos;
> > >
> > > +	if (pages > (1 << VIRTIO_BALLOON_NR_PFN_BITS)) {
> > > +		/* when the length field can't contain pages, set it to 0 to
> > 
> > /*
> >  * Multi-line
> >  * comments
> >  * should look like this.
> >  */
> > 
> > Also, pls start sentences with an upper-case letter.
> > 
> 
> Sorry for that.
> 
> > > +		 * indicate the actual length is in the next __le64;
> > > +		 */
> > 
> > This is part of the interface so should be documented as such.
> > 
> > > +		*range = cpu_to_le64((base_pfn <<
> > > +				VIRTIO_BALLOON_NR_PFN_BITS) | 0);
> > > +		*(range + 1) = cpu_to_le64(pages);
> > > +		vb->resp_pos += 2;
> > 
> > Pls use structs for this kind of stuff.
> 
> I am not sure if you mean to use 
> 
> struct  range {
>  	__le64 pfn: 52;
> 	__le64 nr_page: 12
> }
> Instead of the shift operation?

Not just that. You want to add a pages field as well.

Generally describe the format in the header in some way
so host and guest can easily stay in sync.

All the pointer math and void * means we get zero type
safety and I'm not happy about it.


> I didn't use this way because I don't want to include 'virtio-balloon.h' in page_alloc.c,
> or copy the define of this struct in page_alloc.c
> 
> Thanks!
> Liang


It's not good that virtio format seeps out to page_alloc anyway.
If unavoidable it is not a good idea to try to hide this fact,
people will assume they can change the format at will.

-- 
MST

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#1562372

> On Wed, Jan 18, 2017 at 04:56:58AM +0000, Li, Liang Z wrote:
> > > > -	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> > > > -	virtqueue_kick(vq);
> > > > +static void do_set_resp_bitmap(struct virtio_balloon *vb,
> > > > +		unsigned long base_pfn, int pages)
> > > >
> > > > -	/* When host has read buffer, this completes via balloon_ack */
> > > > -	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> > > > +{
> > > > +	__le64 *range = vb->resp_data + vb->resp_pos;
> > > >
> > > > +	if (pages > (1 << VIRTIO_BALLOON_NR_PFN_BITS)) {
> > > > +		/* when the length field can't contain pages, set it to 0 to
> > >
> > > /*
> > >  * Multi-line
> > >  * comments
> > >  * should look like this.
> > >  */
> > >
> > > Also, pls start sentences with an upper-case letter.
> > >
> >
> > Sorry for that.
> >
> > > > +		 * indicate the actual length is in the next __le64;
> > > > +		 */
> > >
> > > This is part of the interface so should be documented as such.
> > >
> > > > +		*range = cpu_to_le64((base_pfn <<
> > > > +				VIRTIO_BALLOON_NR_PFN_BITS) | 0);
> > > > +		*(range + 1) = cpu_to_le64(pages);
> > > > +		vb->resp_pos += 2;
> > >
> > > Pls use structs for this kind of stuff.
> >
> > I am not sure if you mean to use
> >
> > struct  range {
> >  	__le64 pfn: 52;
> > 	__le64 nr_page: 12
> > }
> > Instead of the shift operation?
> 
> Not just that. You want to add a pages field as well.
> 

pages field? Could you give more hints?

> Generally describe the format in the header in some way so host and guest
> can easily stay in sync.

'VIRTIO_BALLOON_NR_PFN_BITS' is for this purpose and it will be passed to the
related function in page_alloc.c as a parameter.

Thanks!
Liang
> All the pointer math and void * means we get zero type safety and I'm not
> happy about it.
> 
> It's not good that virtio format seeps out to page_alloc anyway.
> If unavoidable it is not a good idea to try to hide this fact, people will assume
> they can change the format at will.
> 
> --
> MST

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#1563766

On Thu, Jan 19, 2017 at 01:44:36AM +0000, Li, Liang Z wrote:
> > > > > +		*range = cpu_to_le64((base_pfn <<
> > > > > +				VIRTIO_BALLOON_NR_PFN_BITS) | 0);
> > > > > +		*(range + 1) = cpu_to_le64(pages);
> > > > > +		vb->resp_pos += 2;
> > > >
> > > > Pls use structs for this kind of stuff.
> > >
> > > I am not sure if you mean to use
> > >
> > > struct  range {
> > >  	__le64 pfn: 52;
> > > 	__le64 nr_page: 12
> > > }
> > > Instead of the shift operation?
> > 
> > Not just that. You want to add a pages field as well.
> > 
> 
> pages field? Could you give more hints?

Well look how you are formatting it manually above.
There is clearly a structure with two 64 bit fields.
First one includes pfn and 0 (no idea why does | 0 make
sense but that's a separate issue).
Second one includes the pages value.


> > Generally describe the format in the header in some way so host and guest
> > can easily stay in sync.
> 
> 'VIRTIO_BALLOON_NR_PFN_BITS' is for this purpose and it will be passed to the
> related function in page_alloc.c as a parameter.
> 
> Thanks!
> Liang
> > All the pointer math and void * means we get zero type safety and I'm not
> > happy about it.
> > 
> > It's not good that virtio format seeps out to page_alloc anyway.
> > If unavoidable it is not a good idea to try to hide this fact, people will assume
> > they can change the format at will.
> > 
> > --
> > MST

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