Re: [Xen-devel] [PATCH v2 3/3] xen-blkfront: dynamic configuration of per-vbd resources

[Roger Pau Monné]

On Tue, Jul 26, 2016 at 04:58:10PM +0800, Bob Liu wrote:
> 
> On 07/26/2016 04:44 PM, Roger Pau Monné wrote:
> > On Tue, Jul 26, 2016 at 01:19:37PM +0800, Bob Liu wrote:
> >> The current VBD layer reserves buffer space for each attached device based 
> >> on
> >> three statically configured settings which are read at boot time.
> >>  * max_indirect_segs: Maximum amount of segments.
> >>  * max_ring_page_order: Maximum order of pages to be used for the shared 
> >> ring.
> >>  * max_queues: Maximum of queues(rings) to be used.
> >>
> >> But the storage backend, workload, and guest memory result in very 
> >> different
> >> tuning requirements. It's impossible to centrally predict application
> >> characteristics so it's best to leave allow the settings can be dynamiclly
> >> adjusted based on workload inside the Guest.
> >>
> >> Usage:
> >> Show current values:
> >> cat /sys/devices/vbd-xxx/max_indirect_segs
> >> cat /sys/devices/vbd-xxx/max_ring_page_order
> >> cat /sys/devices/vbd-xxx/max_queues
> >>
> >> Write new values:
> >> echo  > /sys/devices/vbd-xxx/max_indirect_segs
> >> echo  > /sys/devices/vbd-xxx/max_ring_page_order
> >> echo  > /sys/devices/vbd-xxx/max_queues
> >>
> >> Signed-off-by: Bob Liu 
> >> --
> >> v2: Rename to max_ring_page_order and rm the waiting code suggested by 
> >> Roger.
> >> ---
> >>  drivers/block/xen-blkfront.c |  275 
> >> +-
> >>  1 file changed, 269 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> >> index 1b4c380..ff5ebe5 100644
> >> --- a/drivers/block/xen-blkfront.c
> >> +++ b/drivers/block/xen-blkfront.c
> >> @@ -212,6 +212,11 @@ struct blkfront_info
> >>/* Save uncomplete reqs and bios for migration. */
> >>struct list_head requests;
> >>struct bio_list bio_list;
> >> +  /* For dynamic configuration. */
> >> +  unsigned int reconfiguring:1;
> >> +  int new_max_indirect_segments;
> > 
> > Can't you just use max_indirect_segments? Is it really needed to introduce 
> > a 
> > new struct member?
> > 
> >> +  int max_ring_page_order;
> >> +  int max_queues;
> 
> Do you mean also get rid of these two new struct members?
> I'll think about that.

Oh no, those two are fine, and AFAICT are needed because now every blkfront 
instance can have it's own max number of queues or ring pages. What I think 
can be removed is the introduction of new_max_indirect_segments, and instead 
just use the already available max_indirect_segments field in that same 
struct.

Roger.

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Re: [Xen-devel] [PATCH v2 3/3] xen-blkfront: dynamic configuration of per-vbd resources

[Bob Liu]

On 07/26/2016 04:44 PM, Roger Pau Monné wrote:
> On Tue, Jul 26, 2016 at 01:19:37PM +0800, Bob Liu wrote:
>> The current VBD layer reserves buffer space for each attached device based on
>> three statically configured settings which are read at boot time.
>>  * max_indirect_segs: Maximum amount of segments.
>>  * max_ring_page_order: Maximum order of pages to be used for the shared 
>> ring.
>>  * max_queues: Maximum of queues(rings) to be used.
>>
>> But the storage backend, workload, and guest memory result in very different
>> tuning requirements. It's impossible to centrally predict application
>> characteristics so it's best to leave allow the settings can be dynamiclly
>> adjusted based on workload inside the Guest.
>>
>> Usage:
>> Show current values:
>> cat /sys/devices/vbd-xxx/max_indirect_segs
>> cat /sys/devices/vbd-xxx/max_ring_page_order
>> cat /sys/devices/vbd-xxx/max_queues
>>
>> Write new values:
>> echo  > /sys/devices/vbd-xxx/max_indirect_segs
>> echo  > /sys/devices/vbd-xxx/max_ring_page_order
>> echo  > /sys/devices/vbd-xxx/max_queues
>>
>> Signed-off-by: Bob Liu 
>> --
>> v2: Rename to max_ring_page_order and rm the waiting code suggested by Roger.
>> ---
>>  drivers/block/xen-blkfront.c |  275 
>> +-
>>  1 file changed, 269 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 1b4c380..ff5ebe5 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -212,6 +212,11 @@ struct blkfront_info
>>  /* Save uncomplete reqs and bios for migration. */
>>  struct list_head requests;
>>  struct bio_list bio_list;
>> +/* For dynamic configuration. */
>> +unsigned int reconfiguring:1;
>> +int new_max_indirect_segments;
> 
> Can't you just use max_indirect_segments? Is it really needed to introduce a 
> new struct member?
> 
>> +int max_ring_page_order;
>> +int max_queues;

Do you mean also get rid of these two new struct members?
I'll think about that.

>>  };
>>  
>>  static unsigned int nr_minors;
>> @@ -1350,6 +1355,31 @@ static void blkif_free(struct blkfront_info *info, 
>> int suspend)
>>  for (i = 0; i < info->nr_rings; i++)
>>  blkif_free_ring(>rinfo[i]);
>>  
>> +/* Remove old xenstore nodes. */
>> +if (info->nr_ring_pages > 1)
>> +xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-page-order");
>> +
>> +if (info->nr_rings == 1) {
>> +if (info->nr_ring_pages == 1) {
>> +xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-ref");
>> +} else {
>> +for (i = 0; i < info->nr_ring_pages; i++) {
>> +char ring_ref_name[RINGREF_NAME_LEN];
>> +
>> +snprintf(ring_ref_name, RINGREF_NAME_LEN, 
>> "ring-ref%u", i);
>> +xenbus_rm(XBT_NIL, info->xbdev->nodename, 
>> ring_ref_name);
>> +}
>> +}
>> +} else {
>> +xenbus_rm(XBT_NIL, info->xbdev->nodename, 
>> "multi-queue-num-queues");
>> +
>> +for (i = 0; i < info->nr_rings; i++) {
>> +char queuename[QUEUE_NAME_LEN];
>> +
>> +snprintf(queuename, QUEUE_NAME_LEN, "queue-%u", i);
>> +xenbus_rm(XBT_NIL, info->xbdev->nodename, queuename);
>> +}
>> +}
>>  kfree(info->rinfo);
>>  info->rinfo = NULL;
>>  info->nr_rings = 0;
>> @@ -1763,15 +1793,21 @@ static int talk_to_blkback(struct xenbus_device *dev,
>>  const char *message = NULL;
>>  struct xenbus_transaction xbt;
>>  int err;
>> -unsigned int i, max_page_order = 0;
>> +unsigned int i, backend_max_order = 0;
>>  unsigned int ring_page_order = 0;
>>  
>>  err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
>> -   "max-ring-page-order", "%u", _page_order);
>> +   "max-ring-page-order", "%u", _max_order);
>>  if (err != 1)
>>  info->nr_ring_pages = 1;
>>  else {
>> -ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
>> +if (info->max_ring_page_order) {
>> +/* Dynamic configured through /sys. */
>> +BUG_ON(info->max_ring_page_order > backend_max_order);
> 
> Maybe I'm missing something, but I don't think you can BUG here. The 
> following flow for example will trigger this BUG:
> 

You are right, this BUG will be triggered after removed the waiting code in 
this version.
Will be updated.

>  - Admin sets max_ring_page_order = 2 from sysfs, frontend reconfigures.
>  - VM is migrated to a new host without multipage ring support.
>  - BUG will trigger on reconnection (because backend_max_order == 1 and 
>max_ring_page_order == 2).
> 


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Re: [Xen-devel] [PATCH v2 3/3] xen-blkfront: dynamic configuration of per-vbd resources

[Roger Pau Monné]

On Tue, Jul 26, 2016 at 01:19:37PM +0800, Bob Liu wrote:
> The current VBD layer reserves buffer space for each attached device based on
> three statically configured settings which are read at boot time.
>  * max_indirect_segs: Maximum amount of segments.
>  * max_ring_page_order: Maximum order of pages to be used for the shared ring.
>  * max_queues: Maximum of queues(rings) to be used.
> 
> But the storage backend, workload, and guest memory result in very different
> tuning requirements. It's impossible to centrally predict application
> characteristics so it's best to leave allow the settings can be dynamiclly
> adjusted based on workload inside the Guest.
> 
> Usage:
> Show current values:
> cat /sys/devices/vbd-xxx/max_indirect_segs
> cat /sys/devices/vbd-xxx/max_ring_page_order
> cat /sys/devices/vbd-xxx/max_queues
> 
> Write new values:
> echo  > /sys/devices/vbd-xxx/max_indirect_segs
> echo  > /sys/devices/vbd-xxx/max_ring_page_order
> echo  > /sys/devices/vbd-xxx/max_queues
> 
> Signed-off-by: Bob Liu 
> --
> v2: Rename to max_ring_page_order and rm the waiting code suggested by Roger.
> ---
>  drivers/block/xen-blkfront.c |  275 
> +-
>  1 file changed, 269 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 1b4c380..ff5ebe5 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -212,6 +212,11 @@ struct blkfront_info
>   /* Save uncomplete reqs and bios for migration. */
>   struct list_head requests;
>   struct bio_list bio_list;
> + /* For dynamic configuration. */
> + unsigned int reconfiguring:1;
> + int new_max_indirect_segments;

Can't you just use max_indirect_segments? Is it really needed to introduce a 
new struct member?

> + int max_ring_page_order;
> + int max_queues;
>  };
>  
>  static unsigned int nr_minors;
> @@ -1350,6 +1355,31 @@ static void blkif_free(struct blkfront_info *info, int 
> suspend)
>   for (i = 0; i < info->nr_rings; i++)
>   blkif_free_ring(>rinfo[i]);
>  
> + /* Remove old xenstore nodes. */
> + if (info->nr_ring_pages > 1)
> + xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-page-order");
> +
> + if (info->nr_rings == 1) {
> + if (info->nr_ring_pages == 1) {
> + xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-ref");
> + } else {
> + for (i = 0; i < info->nr_ring_pages; i++) {
> + char ring_ref_name[RINGREF_NAME_LEN];
> +
> + snprintf(ring_ref_name, RINGREF_NAME_LEN, 
> "ring-ref%u", i);
> + xenbus_rm(XBT_NIL, info->xbdev->nodename, 
> ring_ref_name);
> + }
> + }
> + } else {
> + xenbus_rm(XBT_NIL, info->xbdev->nodename, 
> "multi-queue-num-queues");
> +
> + for (i = 0; i < info->nr_rings; i++) {
> + char queuename[QUEUE_NAME_LEN];
> +
> + snprintf(queuename, QUEUE_NAME_LEN, "queue-%u", i);
> + xenbus_rm(XBT_NIL, info->xbdev->nodename, queuename);
> + }
> + }
>   kfree(info->rinfo);
>   info->rinfo = NULL;
>   info->nr_rings = 0;
> @@ -1763,15 +1793,21 @@ static int talk_to_blkback(struct xenbus_device *dev,
>   const char *message = NULL;
>   struct xenbus_transaction xbt;
>   int err;
> - unsigned int i, max_page_order = 0;
> + unsigned int i, backend_max_order = 0;
>   unsigned int ring_page_order = 0;
>  
>   err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> -"max-ring-page-order", "%u", _page_order);
> +"max-ring-page-order", "%u", _max_order);
>   if (err != 1)
>   info->nr_ring_pages = 1;
>   else {
> - ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
> + if (info->max_ring_page_order) {
> + /* Dynamic configured through /sys. */
> + BUG_ON(info->max_ring_page_order > backend_max_order);

Maybe I'm missing something, but I don't think you can BUG here. The 
following flow for example will trigger this BUG:

 - Admin sets max_ring_page_order = 2 from sysfs, frontend reconfigures.
 - VM is migrated to a new host without multipage ring support.
 - BUG will trigger on reconnection (because backend_max_order == 1 and 
   max_ring_page_order == 2).

Roger.

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[Xen-devel] [PATCH v2 3/3] xen-blkfront: dynamic configuration of per-vbd resources

[Bob Liu]

The current VBD layer reserves buffer space for each attached device based on
three statically configured settings which are read at boot time.
 * max_indirect_segs: Maximum amount of segments.
 * max_ring_page_order: Maximum order of pages to be used for the shared ring.
 * max_queues: Maximum of queues(rings) to be used.

But the storage backend, workload, and guest memory result in very different
tuning requirements. It's impossible to centrally predict application
characteristics so it's best to leave allow the settings can be dynamiclly
adjusted based on workload inside the Guest.

Usage:
Show current values:
cat /sys/devices/vbd-xxx/max_indirect_segs
cat /sys/devices/vbd-xxx/max_ring_page_order
cat /sys/devices/vbd-xxx/max_queues

Write new values:
echo  > /sys/devices/vbd-xxx/max_indirect_segs
echo  > /sys/devices/vbd-xxx/max_ring_page_order
echo  > /sys/devices/vbd-xxx/max_queues

Signed-off-by: Bob Liu 
--
v2: Rename to max_ring_page_order and rm the waiting code suggested by Roger.
---
 drivers/block/xen-blkfront.c |  275 +-
 1 file changed, 269 insertions(+), 6 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 1b4c380..ff5ebe5 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -212,6 +212,11 @@ struct blkfront_info
/* Save uncomplete reqs and bios for migration. */
struct list_head requests;
struct bio_list bio_list;
+   /* For dynamic configuration. */
+   unsigned int reconfiguring:1;
+   int new_max_indirect_segments;
+   int max_ring_page_order;
+   int max_queues;
 };
 
 static unsigned int nr_minors;
@@ -1350,6 +1355,31 @@ static void blkif_free(struct blkfront_info *info, int 
suspend)
for (i = 0; i < info->nr_rings; i++)
blkif_free_ring(>rinfo[i]);
 
+   /* Remove old xenstore nodes. */
+   if (info->nr_ring_pages > 1)
+   xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-page-order");
+
+   if (info->nr_rings == 1) {
+   if (info->nr_ring_pages == 1) {
+   xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-ref");
+   } else {
+   for (i = 0; i < info->nr_ring_pages; i++) {
+   char ring_ref_name[RINGREF_NAME_LEN];
+
+   snprintf(ring_ref_name, RINGREF_NAME_LEN, 
"ring-ref%u", i);
+   xenbus_rm(XBT_NIL, info->xbdev->nodename, 
ring_ref_name);
+   }
+   }
+   } else {
+   xenbus_rm(XBT_NIL, info->xbdev->nodename, 
"multi-queue-num-queues");
+
+   for (i = 0; i < info->nr_rings; i++) {
+   char queuename[QUEUE_NAME_LEN];
+
+   snprintf(queuename, QUEUE_NAME_LEN, "queue-%u", i);
+   xenbus_rm(XBT_NIL, info->xbdev->nodename, queuename);
+   }
+   }
kfree(info->rinfo);
info->rinfo = NULL;
info->nr_rings = 0;
@@ -1763,15 +1793,21 @@ static int talk_to_blkback(struct xenbus_device *dev,
const char *message = NULL;
struct xenbus_transaction xbt;
int err;
-   unsigned int i, max_page_order = 0;
+   unsigned int i, backend_max_order = 0;
unsigned int ring_page_order = 0;
 
err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
-  "max-ring-page-order", "%u", _page_order);
+  "max-ring-page-order", "%u", _max_order);
if (err != 1)
info->nr_ring_pages = 1;
else {
-   ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
+   if (info->max_ring_page_order) {
+   /* Dynamic configured through /sys. */
+   BUG_ON(info->max_ring_page_order > backend_max_order);
+   ring_page_order = info->max_ring_page_order;
+   } else
+   /* Default. */
+   ring_page_order = min(xen_blkif_max_ring_order, 
backend_max_order);
info->nr_ring_pages = 1 << ring_page_order;
}
 
@@ -1894,7 +1930,14 @@ static int negotiate_mq(struct blkfront_info *info)
if (err < 0)
backend_max_queues = 1;
 
-   info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
+   if (info->max_queues) {
+   /* Dynamic configured through /sys */
+   BUG_ON(info->max_queues > backend_max_queues);
+   info->nr_rings = info->max_queues;
+   } else
+   /* Default. */
+   info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
+
/* We need at least one ring. */
if (!info->nr_rings)
info->nr_rings = 1;
@@ -2352,11 +2395,197 @@ static void blkfront_gather_backend_features(struct 
blkfront_info *info)