[virtio-dev] RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-05 Thread Wang, Wei W 
On Friday, April 6, 2018 2:30 AM, Michael S. Tsirkin wrote:
> On Thu, Apr 05, 2018 at 03:47:28PM +, Wang, Wei W wrote:
> > On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote:
> > > On Thu, Apr 05, 2018 at 02:05:03AM +, Wang, Wei W wrote:
> > > > On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> > > > > On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> > > > > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > > > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > > > > I'm afraid the driver couldn't be aware if the added hints are
> > > > > > stale or not,
> > > > >
> > > > >
> > > > > No - I mean that driver has code that compares two values and
> > > > > stops reporting. Can one of the values be stale?
> > > >
> > > > The driver compares "vb->cmd_id_use != vb->cmd_id_received" to
> > > > decide if it needs to stop reporting hints, and cmd_id_received is
> > > > what the driver reads from host (host notifies the driver to read
> > > > for the latest value). If host sends a new cmd id, it will notify
> > > > the guest to read again. I'm not sure how that could be a stale
> > > > cmd id (or maybe I misunderstood your point here?)
> > > >
> > > > Best,
> > > > Wei
> > >
> > > The comparison is done in one thread, the update in another one.
> >
> > I think this isn't something that could be solved by adding a lock,
> > unless host waits for the driver's ACK about finishing the update
> > (this is not agreed in the QEMU part discussion).
> >
> > Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we
> don't
> > need to worry about that using DMA api case (we only have gpa added to
> > the vq, and having some entries stay in the vq seems fine). For this
> > feature, I think it would not work with F_IOMMU enabled either.
> 
> Adding a code comment explaining all this might be a good idea.

Thanks, will do.

Best,
Wei

-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-05 Thread Michael S. Tsirkin 
On Thu, Apr 05, 2018 at 03:47:28PM +, Wang, Wei W wrote:
> On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote:
> > On Thu, Apr 05, 2018 at 02:05:03AM +, Wang, Wei W wrote:
> > > On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> > > > On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> > > > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > > > I'm afraid the driver couldn't be aware if the added hints are
> > > > > stale or not,
> > > >
> > > >
> > > > No - I mean that driver has code that compares two values and stops
> > > > reporting. Can one of the values be stale?
> > >
> > > The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide
> > > if it needs to stop reporting hints, and cmd_id_received is what the
> > > driver reads from host (host notifies the driver to read for the
> > > latest value). If host sends a new cmd id, it will notify the guest to
> > > read again. I'm not sure how that could be a stale cmd id (or maybe I
> > > misunderstood your point here?)
> > >
> > > Best,
> > > Wei
> > 
> > The comparison is done in one thread, the update in another one.
> 
> I think this isn't something that could be solved by adding a lock,
> unless host waits for the driver's ACK about finishing the update
> (this is not agreed in the QEMU part discussion).
> 
> Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we don't
> need to worry about that using DMA api case (we only have gpa added to
> the vq, and having some entries stay in the vq seems fine). For this
> feature, I think it would not work with F_IOMMU enabled either.

Adding a code comment explaining all this might be a good idea.

> If there is any further need (I couldn't think of a need so far), I
> think we could consider to let host inject a vq interrupt at some
> point, and then the driver handler can do the virtqueue_get_buf work.
> 
> Best,
> Wei





-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-05 Thread Wang, Wei W 
On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote:
> On Thu, Apr 05, 2018 at 02:05:03AM +, Wang, Wei W wrote:
> > On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> > > On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> > > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > > I'm afraid the driver couldn't be aware if the added hints are
> > > > stale or not,
> > >
> > >
> > > No - I mean that driver has code that compares two values and stops
> > > reporting. Can one of the values be stale?
> >
> > The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide
> > if it needs to stop reporting hints, and cmd_id_received is what the
> > driver reads from host (host notifies the driver to read for the
> > latest value). If host sends a new cmd id, it will notify the guest to
> > read again. I'm not sure how that could be a stale cmd id (or maybe I
> > misunderstood your point here?)
> >
> > Best,
> > Wei
> 
> The comparison is done in one thread, the update in another one.

I think this isn't something that could be solved by adding a lock, unless host 
waits for the driver's ACK about finishing the update (this is not agreed in 
the QEMU part discussion).

Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we don't need to 
worry about that using DMA api case (we only have gpa added to the vq, and 
having some entries stay in the vq seems fine). For this feature, I think it 
would not work with F_IOMMU enabled either.

If there is any further need (I couldn't think of a need so far), I think we 
could consider to let host inject a vq interrupt at some point, and then the 
driver handler can do the virtqueue_get_buf work.

Best,
Wei


-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-05 Thread Michael S. Tsirkin 
On Thu, Apr 05, 2018 at 02:05:03AM +, Wang, Wei W wrote:
> On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> > On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > I'm afraid the driver couldn't be aware if the added hints are stale
> > > or not,
> > 
> > 
> > No - I mean that driver has code that compares two values and stops
> > reporting. Can one of the values be stale?
> 
> The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide if it 
> needs to stop reporting hints, and cmd_id_received is what the driver reads 
> from host (host notifies the driver to read for the latest value). If host 
> sends a new cmd id, it will notify the guest to read again. I'm not sure how 
> that could be a stale cmd id (or maybe I misunderstood your point here?)
> 
> Best,
> Wei

The comparison is done in one thread, the update in another one.

-- 
MST

-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-04 Thread Wang, Wei W 
On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > I'm afraid the driver couldn't be aware if the added hints are stale
> > or not,
> 
> 
> No - I mean that driver has code that compares two values and stops
> reporting. Can one of the values be stale?

The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide if it 
needs to stop reporting hints, and cmd_id_received is what the driver reads 
from host (host notifies the driver to read for the latest value). If host 
sends a new cmd id, it will notify the guest to read again. I'm not sure how 
that could be a stale cmd id (or maybe I misunderstood your point here?)

Best,
Wei

-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-04 Thread Michael S. Tsirkin 
On Thu, Apr 05, 2018 at 12:30:27AM +, Wang, Wei W wrote:
> On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > > > +static int add_one_sg(struct virtqueue *vq, unsigned long pfn,
> > > > > +uint32_t len) {
> > > > > + struct scatterlist sg;
> > > > > + unsigned int unused;
> > > > > +
> > > > > + sg_init_table(, 1);
> > > > > + sg_set_page(, pfn_to_page(pfn), len, 0);
> > > > > +
> > > > > + /* Detach all the used buffers from the vq */
> > > > > + while (virtqueue_get_buf(vq, ))
> > > > > + ;
> > > > > +
> > > > > + /*
> > > > > +  * Since this is an optimization feature, losing a couple of 
> > > > > free
> > > > > +  * pages to report isn't important. We simply return without 
> > > > > adding
> > > > > +  * the page hint if the vq is full.
> > > > why not stop scanning of following pages though?
> > >
> > > Because continuing to send hints is a way to deliver the maximum
> > > possible hints to host. For example, host may have a delay in taking
> > > hints at some point, and then it resumes to take hints soon. If the
> > > driver does not stop when the vq is full, it will be able to put more
> > > hints to the vq once the vq has available entries to add.
> > 
> > What this appears to be is just lack of coordination between host and guest.
> > 
> > But meanwhile you are spending cycles walking the list uselessly.
> > Instead of trying nilly-willy, the standard thing to do is to wait for host 
> > to
> > consume an entry and proceed.
> > 
> > Coding it up might be tricky, so it's probably acceptable as is for now, but
> > please replace the justification about with a TODO entry that we should
> > synchronize with the host.
> 
> Thanks. I plan to add
> 
> TODO: The current implementation could be further improved by stopping the 
> reporting when the vq is full and continuing the reporting when host notifies 
> that there are available entries for the driver to add.

... that entries have been used.

> 
> > 
> > 
> > >
> > > >
> > > > > +  * We are adding one entry each time, which essentially results 
> > > > > in no
> > > > > +  * memory allocation, so the GFP_KERNEL flag below can be 
> > > > > ignored.
> > > > > +  * Host works by polling the free page vq for hints after 
> > > > > sending the
> > > > > +  * starting cmd id, so the driver doesn't need to kick after 
> > > > > filling
> > > > > +  * the vq.
> > > > > +  * Lastly, there is always one entry reserved for the cmd id to 
> > > > > use.
> > > > > +  */
> > > > > + if (vq->num_free > 1)
> > > > > + return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
> > > > > +
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int virtio_balloon_send_free_pages(void *opaque, unsigned long
> > pfn,
> > > > > +unsigned long nr_pages)
> > > > > +{
> > > > > + struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
> > > > > + uint32_t len = nr_pages << PAGE_SHIFT;
> > > > > +
> > > > > + /*
> > > > > +  * If a stop id or a new cmd id was just received from host, 
> > > > > stop
> > > > > +  * the reporting, and return 1 to indicate an active stop.
> > > > > +  */
> > > > > + if (virtio32_to_cpu(vb->vdev, vb->cmd_id_use) != vb-
> > >cmd_id_received)
> > > > > + return 1;
> > 
> > functions returning int should return 0 or -errno on failure, positive 
> > return
> > code should indicate progress.
> > 
> > If you want a boolean, use bool pls.
> 
> OK. I plan to change 1  to -EBUSY to indicate the case that host actively 
> asks the driver to stop reporting (This makes the callback return value type 
> consistent with walk_free_mem_block). 
> 

something like EINTR might be a better fit.

> 
> > 
> > 
> > > > > +
> > > > this access to cmd_id_use and cmd_id_received without locks bothers
> > > > me. Pls document why it's safe.
> > >
> > > OK. Probably we could add below to the above comments:
> > >
> > > cmd_id_use and cmd_id_received don't need to be accessed under locks
> > > because the reporting does not have to stop immediately before
> > > cmd_id_received is changed (i.e. when host requests to stop). That is,
> > > reporting more hints after host requests to stop isn't an issue for
> > > this optimization feature, because host will simply drop the stale
> > > hints next time when it needs a new reporting.
> > 
> > What about the other direction? Can this observe a stale value and exit
> > erroneously?
> 
> I'm afraid the driver couldn't be aware if the added hints are stale or not,


No - I mean that driver has code that compares two values
and stops reporting. Can one of the values be stale?

> because host and guest actions happen asynchronously. That is,

[virtio-dev] RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-04 Thread Wang, Wei W 
On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > > +static int add_one_sg(struct virtqueue *vq, unsigned long pfn,
> > > > +uint32_t len) {
> > > > +   struct scatterlist sg;
> > > > +   unsigned int unused;
> > > > +
> > > > +   sg_init_table(, 1);
> > > > +   sg_set_page(, pfn_to_page(pfn), len, 0);
> > > > +
> > > > +   /* Detach all the used buffers from the vq */
> > > > +   while (virtqueue_get_buf(vq, ))
> > > > +   ;
> > > > +
> > > > +   /*
> > > > +* Since this is an optimization feature, losing a couple of 
> > > > free
> > > > +* pages to report isn't important. We simply return without 
> > > > adding
> > > > +* the page hint if the vq is full.
> > > why not stop scanning of following pages though?
> >
> > Because continuing to send hints is a way to deliver the maximum
> > possible hints to host. For example, host may have a delay in taking
> > hints at some point, and then it resumes to take hints soon. If the
> > driver does not stop when the vq is full, it will be able to put more
> > hints to the vq once the vq has available entries to add.
> 
> What this appears to be is just lack of coordination between host and guest.
> 
> But meanwhile you are spending cycles walking the list uselessly.
> Instead of trying nilly-willy, the standard thing to do is to wait for host to
> consume an entry and proceed.
> 
> Coding it up might be tricky, so it's probably acceptable as is for now, but
> please replace the justification about with a TODO entry that we should
> synchronize with the host.

Thanks. I plan to add

TODO: The current implementation could be further improved by stopping the 
reporting when the vq is full and continuing the reporting when host notifies 
that there are available entries for the driver to add.


> 
> 
> >
> > >
> > > > +* We are adding one entry each time, which essentially results 
> > > > in no
> > > > +* memory allocation, so the GFP_KERNEL flag below can be 
> > > > ignored.
> > > > +* Host works by polling the free page vq for hints after 
> > > > sending the
> > > > +* starting cmd id, so the driver doesn't need to kick after 
> > > > filling
> > > > +* the vq.
> > > > +* Lastly, there is always one entry reserved for the cmd id to 
> > > > use.
> > > > +*/
> > > > +   if (vq->num_free > 1)
> > > > +   return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
> > > > +
> > > > +   return 0;
> > > > +}
> > > > +
> > > > +static int virtio_balloon_send_free_pages(void *opaque, unsigned long
> pfn,
> > > > +  unsigned long nr_pages)
> > > > +{
> > > > +   struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
> > > > +   uint32_t len = nr_pages << PAGE_SHIFT;
> > > > +
> > > > +   /*
> > > > +* If a stop id or a new cmd id was just received from host, 
> > > > stop
> > > > +* the reporting, and return 1 to indicate an active stop.
> > > > +*/
> > > > +   if (virtio32_to_cpu(vb->vdev, vb->cmd_id_use) != vb-
> >cmd_id_received)
> > > > +   return 1;
> 
> functions returning int should return 0 or -errno on failure, positive return
> code should indicate progress.
> 
> If you want a boolean, use bool pls.

OK. I plan to change 1  to -EBUSY to indicate the case that host actively asks 
the driver to stop reporting (This makes the callback return value type 
consistent with walk_free_mem_block). 



> 
> 
> > > > +
> > > this access to cmd_id_use and cmd_id_received without locks bothers
> > > me. Pls document why it's safe.
> >
> > OK. Probably we could add below to the above comments:
> >
> > cmd_id_use and cmd_id_received don't need to be accessed under locks
> > because the reporting does not have to stop immediately before
> > cmd_id_received is changed (i.e. when host requests to stop). That is,
> > reporting more hints after host requests to stop isn't an issue for
> > this optimization feature, because host will simply drop the stale
> > hints next time when it needs a new reporting.
> 
> What about the other direction? Can this observe a stale value and exit
> erroneously?

I'm afraid the driver couldn't be aware if the added hints are stale or not, 
because host and guest actions happen asynchronously. That is, host side 
iothread stops taking hints as soon as the migration thread asks to stop, it 
doesn't wait for any ACK from the driver to stop (as we discussed before, host 
couldn't always assume that the driver is in a responsive state).

Btw, we also don't need to worry about any memory left in the vq, since only 
addresses are added to the vq, there is no real memory allocations.

Best,
Wei

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-04 Thread Michael S. Tsirkin 
On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > +static int add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t 
> > > len)
> > > +{
> > > + struct scatterlist sg;
> > > + unsigned int unused;
> > > +
> > > + sg_init_table(, 1);
> > > + sg_set_page(, pfn_to_page(pfn), len, 0);
> > > +
> > > + /* Detach all the used buffers from the vq */
> > > + while (virtqueue_get_buf(vq, ))
> > > + ;
> > > +
> > > + /*
> > > +  * Since this is an optimization feature, losing a couple of free
> > > +  * pages to report isn't important. We simply return without adding
> > > +  * the page hint if the vq is full.
> > why not stop scanning of following pages though?
> 
> Because continuing to send hints is a way to deliver the maximum possible
> hints to host. For example, host may have a delay in taking hints at some
> point, and then it resumes to take hints soon. If the driver does not stop
> when the vq is full, it will be able to put more hints to the vq once the vq
> has available entries to add.

What this appears to be is just lack of coordination between
host and guest.

But meanwhile you are spending cycles walking the list uselessly.
Instead of trying nilly-willy, the standard thing to do
is to wait for host to consume an entry and proceed.

Coding it up might be tricky, so it's probably acceptable as is
for now, but please replace the justification about with
a TODO entry that we should synchronize with the host.


> 
> > 
> > > +  * We are adding one entry each time, which essentially results in no
> > > +  * memory allocation, so the GFP_KERNEL flag below can be ignored.
> > > +  * Host works by polling the free page vq for hints after sending the
> > > +  * starting cmd id, so the driver doesn't need to kick after filling
> > > +  * the vq.
> > > +  * Lastly, there is always one entry reserved for the cmd id to use.
> > > +  */
> > > + if (vq->num_free > 1)
> > > + return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int virtio_balloon_send_free_pages(void *opaque, unsigned long 
> > > pfn,
> > > +unsigned long nr_pages)
> > > +{
> > > + struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
> > > + uint32_t len = nr_pages << PAGE_SHIFT;
> > > +
> > > + /*
> > > +  * If a stop id or a new cmd id was just received from host, stop
> > > +  * the reporting, and return 1 to indicate an active stop.
> > > +  */
> > > + if (virtio32_to_cpu(vb->vdev, vb->cmd_id_use) != vb->cmd_id_received)
> > > + return 1;

functions returning int should return 0 or -errno on failure,
positive return code should indicate progress.

If you want a boolean, use bool pls.


> > > +
> > this access to cmd_id_use and cmd_id_received without locks
> > bothers me. Pls document why it's safe.
> 
> OK. Probably we could add below to the above comments:
> 
> cmd_id_use and cmd_id_received don't need to be accessed under locks because
> the reporting does not have to stop immediately before cmd_id_received is
> changed (i.e. when host requests to stop). That is, reporting more hints
> after host requests to stop isn't an issue for this optimization feature,
> because host will simply drop the stale hints next time when it needs a new
> reporting.

What about the other direction? Can this observe a stale value and
exit erroneously?

> 
> 
> 
> > 
> > > + return add_one_sg(vb->free_page_vq, pfn, len);
> > > +}
> > > +
> > > +static int send_start_cmd_id(struct virtio_balloon *vb, uint32_t cmd_id)
> > > +{
> > > + struct scatterlist sg;
> > > + struct virtqueue *vq = vb->free_page_vq;
> > > +
> > > + vb->cmd_id_use = cpu_to_virtio32(vb->vdev, cmd_id);
> > > + sg_init_one(, >cmd_id_use, sizeof(vb->cmd_id_use));
> > > + return virtqueue_add_outbuf(vq, , 1, vb, GFP_KERNEL);
> > > +}
> > > +
> > > +static int send_stop_cmd_id(struct virtio_balloon *vb)
> > > +{
> > > + struct scatterlist sg;
> > > + struct virtqueue *vq = vb->free_page_vq;
> > > +
> > > + sg_init_one(, >stop_cmd_id, sizeof(vb->cmd_id_use));
> > why the inconsistency?
> 
> Thanks, will make it consistent.
> 
> Best,
> Wei

-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-03 Thread Wei Wang 

On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:

On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:

+static int add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t len)
+{
+   struct scatterlist sg;
+   unsigned int unused;
+
+   sg_init_table(, 1);
+   sg_set_page(, pfn_to_page(pfn), len, 0);
+
+   /* Detach all the used buffers from the vq */
+   while (virtqueue_get_buf(vq, ))
+   ;
+
+   /*
+* Since this is an optimization feature, losing a couple of free
+* pages to report isn't important. We simply return without adding
+* the page hint if the vq is full.

why not stop scanning of following pages though?


Because continuing to send hints is a way to deliver the maximum 
possible hints to host. For example, host may have a delay in taking 
hints at some point, and then it resumes to take hints soon. If the 
driver does not stop when the vq is full, it will be able to put more 
hints to the vq once the vq has available entries to add.






+* We are adding one entry each time, which essentially results in no
+* memory allocation, so the GFP_KERNEL flag below can be ignored.
+* Host works by polling the free page vq for hints after sending the
+* starting cmd id, so the driver doesn't need to kick after filling
+* the vq.
+* Lastly, there is always one entry reserved for the cmd id to use.
+*/
+   if (vq->num_free > 1)
+   return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
+
+   return 0;
+}
+
+static int virtio_balloon_send_free_pages(void *opaque, unsigned long pfn,
+  unsigned long nr_pages)
+{
+   struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
+   uint32_t len = nr_pages << PAGE_SHIFT;
+
+   /*
+* If a stop id or a new cmd id was just received from host, stop
+* the reporting, and return 1 to indicate an active stop.
+*/
+   if (virtio32_to_cpu(vb->vdev, vb->cmd_id_use) != vb->cmd_id_received)
+   return 1;
+

this access to cmd_id_use and cmd_id_received without locks
bothers me. Pls document why it's safe.


OK. Probably we could add below to the above comments:

cmd_id_use and cmd_id_received don't need to be accessed under locks 
because the reporting does not have to stop immediately before 
cmd_id_received is changed (i.e. when host requests to stop). That is, 
reporting more hints after host requests to stop isn't an issue for this 
optimization feature, because host will simply drop the stale hints next 
time when it needs a new reporting.








+   return add_one_sg(vb->free_page_vq, pfn, len);
+}
+
+static int send_start_cmd_id(struct virtio_balloon *vb, uint32_t cmd_id)
+{
+   struct scatterlist sg;
+   struct virtqueue *vq = vb->free_page_vq;
+
+   vb->cmd_id_use = cpu_to_virtio32(vb->vdev, cmd_id);
+   sg_init_one(, >cmd_id_use, sizeof(vb->cmd_id_use));
+   return virtqueue_add_outbuf(vq, , 1, vb, GFP_KERNEL);
+}
+
+static int send_stop_cmd_id(struct virtio_balloon *vb)
+{
+   struct scatterlist sg;
+   struct virtqueue *vq = vb->free_page_vq;
+
+   sg_init_one(, >stop_cmd_id, sizeof(vb->cmd_id_use));

why the inconsistency?


Thanks, will make it consistent.

Best,
Wei

-
To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org

[virtio-dev] Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-04-03 Thread Michael S. Tsirkin 
On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature indicates the
> support of reporting hints of guest free pages to host via virtio-balloon.
> 
> Host requests the guest to report free page hints by sending a new cmd
> id to the guest via the free_page_report_cmd_id configuration register.
> 
> When the guest starts to report, the first element added to the free page
> vq is the cmd id given by host. When the guest finishes the reporting
> of all the free pages, VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID is added
> to the vq to tell host that the reporting is done. Host polls the free
> page vq after sending the starting cmd id, so the guest doesn't need to
> kick after filling an element to the vq.
> 
> Host may also requests the guest to stop the reporting in advance by
> sending the stop cmd id to the guest via the configuration register.
> 
> Signed-off-by: Wei Wang 
> Signed-off-by: Liang Li 
> Cc: Michael S. Tsirkin 
> Cc: Michal Hocko 
> ---
>  drivers/virtio/virtio_balloon.c | 257 
> +++-
>  include/uapi/linux/virtio_balloon.h |   4 +
>  2 files changed, 225 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index dfe5684..18d24a4 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -51,9 +51,22 @@
>  static struct vfsmount *balloon_mnt;
>  #endif
>  
> +enum virtio_balloon_vq {
> + VIRTIO_BALLOON_VQ_INFLATE,
> + VIRTIO_BALLOON_VQ_DEFLATE,
> + VIRTIO_BALLOON_VQ_STATS,
> + VIRTIO_BALLOON_VQ_FREE_PAGE,
> + VIRTIO_BALLOON_VQ_MAX
> +};
> +
>  struct virtio_balloon {
>   struct virtio_device *vdev;
> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
> +
> + /* Balloon's own wq for cpu-intensive work items */
> + struct workqueue_struct *balloon_wq;
> + /* The free page reporting work item submitted to the balloon wq */
> + struct work_struct report_free_page_work;
>  
>   /* The balloon servicing is delegated to a freezable workqueue. */
>   struct work_struct update_balloon_stats_work;
> @@ -63,6 +76,13 @@ struct virtio_balloon {
>   spinlock_t stop_update_lock;
>   bool stop_update;
>  
> + /* The new cmd id received from host */
> + uint32_t cmd_id_received;
> + /* The cmd id that is in use */
> + __virtio32 cmd_id_use;
> + /* Buffer to store the stop sign */
> + __virtio32 stop_cmd_id;
> +
>   /* Waiting for host to ack the pages we released. */
>   wait_queue_head_t acked;
>  
> @@ -320,17 +340,6 @@ static void stats_handle_request(struct virtio_balloon 
> *vb)
>   virtqueue_kick(vq);
>  }
>  
> -static void virtballoon_changed(struct virtio_device *vdev)
> -{
> - struct virtio_balloon *vb = vdev->priv;
> - unsigned long flags;
> -
> - spin_lock_irqsave(>stop_update_lock, flags);
> - if (!vb->stop_update)
> - queue_work(system_freezable_wq, >update_balloon_size_work);
> - spin_unlock_irqrestore(>stop_update_lock, flags);
> -}
> -
>  static inline s64 towards_target(struct virtio_balloon *vb)
>  {
>   s64 target;
> @@ -347,6 +356,34 @@ static inline s64 towards_target(struct virtio_balloon 
> *vb)
>   return target - vb->num_pages;
>  }
>  
> +static void virtballoon_changed(struct virtio_device *vdev)
> +{
> + struct virtio_balloon *vb = vdev->priv;
> + unsigned long flags;
> + s64 diff = towards_target(vb);
> +
> + if (diff) {
> + spin_lock_irqsave(>stop_update_lock, flags);
> + if (!vb->stop_update)
> + queue_work(system_freezable_wq,
> +>update_balloon_size_work);
> + spin_unlock_irqrestore(>stop_update_lock, flags);
> + }
> +
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + virtio_cread(vdev, struct virtio_balloon_config,
> +  free_page_report_cmd_id, >cmd_id_received);
> + if (vb->cmd_id_received !=
> + VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) {
> + spin_lock_irqsave(>stop_update_lock, flags);
> + if (!vb->stop_update)
> + queue_work(vb->balloon_wq,
> +>report_free_page_work);
> + spin_unlock_irqrestore(>stop_update_lock, flags);
> + }
> + }
> +}
> +
>  static void update_balloon_size(struct virtio_balloon *vb)
>  {
>   u32 actual = vb->num_pages;
> @@ -421,42 +458,163 @@ static void update_balloon_size_func(struct 
> work_struct *work)
>  
>  static int init_vqs(struct virtio_balloon *vb)
>  {
> - struct virtqueue *vqs[3];
> - vq_callback_t