[PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

v1:
  * seg_max default value changing removed

---
The goal is to reduce the amount of requests issued by a guest on
1M reads/writes. This rises the performance up to 4% on that kind of
disk access pattern.

The maximum chunk size to be used for the guest disk accessing is
limited with seg_max parameter, which represents the max amount of
pices in the scatter-geather list in one guest disk request.

Since seg_max is virqueue_size dependent, increasing the virtqueue
size increases seg_max, which, in turn, increases the maximum size
of data to be read/write from a guest disk.

More details in the original problem statment:
https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html

Suggested-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 hw/block/virtio-blk.c | 2 +-
 hw/core/machine.c     | 2 ++
 hw/scsi/virtio-scsi.c | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 09f46ed85f..142863a3b2 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
     DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
                     true),
     DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
-    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
+    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
     DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
     DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
                      IOThread *),
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 2501b540ec..3427d6cf4c 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -28,6 +28,8 @@
 #include "hw/mem/nvdimm.h"
 
 GlobalProperty hw_compat_4_2[] = {
+    { "virtio-blk-device", "queue-size", "128"},
+    { "virtio-scsi-device", "virtqueue_size", "128"},
     { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
     { "virtio-blk-device", "seg-max-adjust", "off"},
     { "virtio-scsi-device", "seg_max_adjust", "off"},
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 3b61563609..472bbd233b 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -965,7 +965,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
 static Property virtio_scsi_properties[] = {
     DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
     DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
-                                         parent_obj.conf.virtqueue_size, 128),
+                                         parent_obj.conf.virtqueue_size, 256),
     DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
                       parent_obj.conf.seg_max_adjust, true),
     DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
-- 
2.17.0

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Philippe Mathieu-Daudé]

Typo 'virtuqueue' in subject.

On 2/13/20 3:59 PM, Denis Plotnikov wrote:
> v1:
>    * seg_max default value changing removed
> 

^^^ This part ...

> ---
> The goal is to reduce the amount of requests issued by a guest on
> 1M reads/writes. This rises the performance up to 4% on that kind of
> disk access pattern.
> 
> The maximum chunk size to be used for the guest disk accessing is
> limited with seg_max parameter, which represents the max amount of
> pices in the scatter-geather list in one guest disk request.
> 
> Since seg_max is virqueue_size dependent, increasing the virtqueue
> size increases seg_max, which, in turn, increases the maximum size
> of data to be read/write from a guest disk.
> 
> More details in the original problem statment:
> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> 
> Suggested-by: Denis V. Lunev <den@openvz.org>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---

... goes here.

>   hw/block/virtio-blk.c | 2 +-
>   hw/core/machine.c     | 2 ++
>   hw/scsi/virtio-scsi.c | 2 +-
>   3 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..142863a3b2 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                       true),
>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                        IOThread *),
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2501b540ec..3427d6cf4c 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -28,6 +28,8 @@
>   #include "hw/mem/nvdimm.h"
>   
>   GlobalProperty hw_compat_4_2[] = {
> +    { "virtio-blk-device", "queue-size", "128"},
> +    { "virtio-scsi-device", "virtqueue_size", "128"},
>       { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
>       { "virtio-blk-device", "seg-max-adjust", "off"},
>       { "virtio-scsi-device", "seg_max_adjust", "off"},
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..472bbd233b 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -965,7 +965,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>   static Property virtio_scsi_properties[] = {
>       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> -                                         parent_obj.conf.virtqueue_size, 128),
> +                                         parent_obj.conf.virtqueue_size, 256),
>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                         parent_obj.conf.seg_max_adjust, true),
>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> 

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Stefan Hajnoczi]

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On Thu, Feb 13, 2020 at 05:59:27PM +0300, Denis Plotnikov wrote:
> v1:
>   * seg_max default value changing removed
> 
> ---
> The goal is to reduce the amount of requests issued by a guest on
> 1M reads/writes. This rises the performance up to 4% on that kind of
> disk access pattern.
> 
> The maximum chunk size to be used for the guest disk accessing is
> limited with seg_max parameter, which represents the max amount of
> pices in the scatter-geather list in one guest disk request.
> 
> Since seg_max is virqueue_size dependent, increasing the virtqueue
> size increases seg_max, which, in turn, increases the maximum size
> of data to be read/write from a guest disk.
> 
> More details in the original problem statment:
> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> 
> Suggested-by: Denis V. Lunev <den@openvz.org>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>  hw/block/virtio-blk.c | 2 +-
>  hw/core/machine.c     | 2 ++
>  hw/scsi/virtio-scsi.c | 2 +-
>  3 files changed, 4 insertions(+), 2 deletions(-)

I fixed up the "virtuqueue" typo in the commit message and the
mis-formatted commit description (git-am(1) stops including lines after
the first "---").

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

On 18.02.2020 16:53, Stefan Hajnoczi wrote:
> On Thu, Feb 13, 2020 at 05:59:27PM +0300, Denis Plotnikov wrote:
>> v1:
>>    * seg_max default value changing removed
>>
>> ---
>> The goal is to reduce the amount of requests issued by a guest on
>> 1M reads/writes. This rises the performance up to 4% on that kind of
>> disk access pattern.
>>
>> The maximum chunk size to be used for the guest disk accessing is
>> limited with seg_max parameter, which represents the max amount of
>> pices in the scatter-geather list in one guest disk request.
>>
>> Since seg_max is virqueue_size dependent, increasing the virtqueue
>> size increases seg_max, which, in turn, increases the maximum size
>> of data to be read/write from a guest disk.
>>
>> More details in the original problem statment:
>> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
>>
>> Suggested-by: Denis V. Lunev <den@openvz.org>
>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>> ---
>>   hw/block/virtio-blk.c | 2 +-
>>   hw/core/machine.c     | 2 ++
>>   hw/scsi/virtio-scsi.c | 2 +-
>>   3 files changed, 4 insertions(+), 2 deletions(-)
> I fixed up the "virtuqueue" typo in the commit message and the
> mis-formatted commit description (git-am(1) stops including lines after
> the first "---").
Actually, I sent the corrected version v3 of the patch last week. But it 
seems it got lost among that gigantic patch flow in the mailing list :)
Thanks for applying!

Denis
>
> Thanks, applied to my block tree:
> https://github.com/stefanha/qemu/commits/block
>
> Stefan

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

On 18.02.2020 16:59, Denis Plotnikov wrote:
>
>
> On 18.02.2020 16:53, Stefan Hajnoczi wrote:
>> On Thu, Feb 13, 2020 at 05:59:27PM +0300, Denis Plotnikov wrote:
>>> v1:
>>>    * seg_max default value changing removed
>>>
>>> ---
>>> The goal is to reduce the amount of requests issued by a guest on
>>> 1M reads/writes. This rises the performance up to 4% on that kind of
>>> disk access pattern.
>>>
>>> The maximum chunk size to be used for the guest disk accessing is
>>> limited with seg_max parameter, which represents the max amount of
>>> pices in the scatter-geather list in one guest disk request.
>>>
>>> Since seg_max is virqueue_size dependent, increasing the virtqueue
>>> size increases seg_max, which, in turn, increases the maximum size
>>> of data to be read/write from a guest disk.
>>>
>>> More details in the original problem statment:
>>> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
>>>
>>> Suggested-by: Denis V. Lunev <den@openvz.org>
>>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>>> ---
>>>   hw/block/virtio-blk.c | 2 +-
>>>   hw/core/machine.c     | 2 ++
>>>   hw/scsi/virtio-scsi.c | 2 +-
>>>   3 files changed, 4 insertions(+), 2 deletions(-)
>> I fixed up the "virtuqueue" typo in the commit message and the
>> mis-formatted commit description (git-am(1) stops including lines after
>> the first "---").
> Actually, I sent the corrected version v3 of the patch last week. But 
> it seems it got lost among that gigantic patch flow in the mailing 
> list :)
> Thanks for applying!
>
> Denis
>>
>> Thanks, applied to my block tree:
>> https://github.com/stefanha/qemu/commits/block
>>
>> Stefan
I'm going to send the test checking the virtqueue-sizes for machine 
types a little bit later.

Denis

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

On 13.02.2020 14:45, Stefan Hajnoczi wrote:
> On Thu, Feb 13, 2020 at 12:28:25PM +0300, Denis Plotnikov wrote:
>>
>> On 13.02.2020 12:08, Stefan Hajnoczi wrote:
>>> On Thu, Feb 13, 2020 at 11:08:35AM +0300, Denis Plotnikov wrote:
>>>> On 12.02.2020 18:43, Stefan Hajnoczi wrote:
>>>>> On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
>>>>>> The goal is to reduce the amount of requests issued by a guest on
>>>>>> 1M reads/writes. This rises the performance up to 4% on that kind of
>>>>>> disk access pattern.
>>>>>>
>>>>>> The maximum chunk size to be used for the guest disk accessing is
>>>>>> limited with seg_max parameter, which represents the max amount of
>>>>>> pices in the scatter-geather list in one guest disk request.
>>>>>>
>>>>>> Since seg_max is virqueue_size dependent, increasing the virtqueue
>>>>>> size increases seg_max, which, in turn, increases the maximum size
>>>>>> of data to be read/write from a guest disk.
>>>>>>
>>>>>> More details in the original problem statment:
>>>>>> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
>>>>>>
>>>>>> Suggested-by: Denis V. Lunev <den@openvz.org>
>>>>>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>>>>>> ---
>>>>>>     hw/block/virtio-blk.c | 4 ++--
>>>>>>     hw/core/machine.c     | 2 ++
>>>>>>     hw/scsi/virtio-scsi.c | 4 ++--
>>>>>>     3 files changed, 6 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>>>>>> index 09f46ed85f..6df3a7a6df 100644
>>>>>> --- a/hw/block/virtio-blk.c
>>>>>> +++ b/hw/block/virtio-blk.c
>>>>>> @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>>>>>         memset(&blkcfg, 0, sizeof(blkcfg));
>>>>>>         virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>>>>>         virtio_stl_p(vdev, &blkcfg.seg_max,
>>>>>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>>>>>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
>>>>> This value must not change on older machine types.
>>>> Yes, that's true, but ..
>>>>> So does this patch
>>>>> need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
>>>>> types get 126 instead of 254?
>>>> If we set seg-max-adjust "on" in older machine types, the setups using them
>>>> and having queue_sizes set , for example, 1024 will also set seg_max to 1024
>>>> - 2 which isn't the expected behavior: older mt didn't change seg_max in
>>>> that case and stuck with 128 - 2.
>>>> So, should we, instead, leave the default 128 - 2, for seg_max?
>>> Argh!  Good point :-).
>>>
>>> How about a seg_max_default property that is initialized to 254 for
>>> modern machines and 126 to old machines?
>> Hmm, but we'll achieve the same but with more code changes, don't we?
>> 254 is because the queue-size is 256. We gonna leave 128-2 for older machine
>> types
>> just for not breaking anything. All other seg_max adjustment is provided by
>> seg_max_adjust which is "on" by default in modern machine types.
>>
>> to summarize:
>>
>> modern mt defaults:
>> seg_max_adjust = on
>> queue_size = 256
>>
>> => default seg_max = 254
>> => changing queue-size will change seg_max = queue_size - 2
>>
>> old mt defaults:
>> seg_max_adjust = off
>> queue_size = 128
>>
>> => default seg_max = 126
>> => changing queue-size won't change seg_max, it's always = 126 like it was
>> before
> You're right!  The only strange case is a modern machine type with
> seg_max_adjust=off, where queue_size will be 256 but seg_max will be
> 126.  But no user would want to disable seg_max_adjust, so it's okay.
>
> I agree with you that the line of code can remain unchanged:
>
>    /*
>     * Only old machine types use seg_max_adjust=off and there the default
>     * value of queue_size is 128.
>     */
>    virtio_stl_p(vdev, &blkcfg.seg_max,
>                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>
> Stefan
Ok, I'll resend the patch sortly
Thanks!

Denis

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Stefan Hajnoczi]

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On Thu, Feb 13, 2020 at 12:28:25PM +0300, Denis Plotnikov wrote:
> 
> 
> On 13.02.2020 12:08, Stefan Hajnoczi wrote:
> > On Thu, Feb 13, 2020 at 11:08:35AM +0300, Denis Plotnikov wrote:
> > > On 12.02.2020 18:43, Stefan Hajnoczi wrote:
> > > > On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
> > > > > The goal is to reduce the amount of requests issued by a guest on
> > > > > 1M reads/writes. This rises the performance up to 4% on that kind of
> > > > > disk access pattern.
> > > > > 
> > > > > The maximum chunk size to be used for the guest disk accessing is
> > > > > limited with seg_max parameter, which represents the max amount of
> > > > > pices in the scatter-geather list in one guest disk request.
> > > > > 
> > > > > Since seg_max is virqueue_size dependent, increasing the virtqueue
> > > > > size increases seg_max, which, in turn, increases the maximum size
> > > > > of data to be read/write from a guest disk.
> > > > > 
> > > > > More details in the original problem statment:
> > > > > https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> > > > > 
> > > > > Suggested-by: Denis V. Lunev <den@openvz.org>
> > > > > Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> > > > > ---
> > > > >    hw/block/virtio-blk.c | 4 ++--
> > > > >    hw/core/machine.c     | 2 ++
> > > > >    hw/scsi/virtio-scsi.c | 4 ++--
> > > > >    3 files changed, 6 insertions(+), 4 deletions(-)
> > > > > 
> > > > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > > > > index 09f46ed85f..6df3a7a6df 100644
> > > > > --- a/hw/block/virtio-blk.c
> > > > > +++ b/hw/block/virtio-blk.c
> > > > > @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
> > > > >        memset(&blkcfg, 0, sizeof(blkcfg));
> > > > >        virtio_stq_p(vdev, &blkcfg.capacity, capacity);
> > > > >        virtio_stl_p(vdev, &blkcfg.seg_max,
> > > > > -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> > > > > +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
> > > > This value must not change on older machine types.
> > > Yes, that's true, but ..
> > > > So does this patch
> > > > need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
> > > > types get 126 instead of 254?
> > > If we set seg-max-adjust "on" in older machine types, the setups using them
> > > and having queue_sizes set , for example, 1024 will also set seg_max to 1024
> > > - 2 which isn't the expected behavior: older mt didn't change seg_max in
> > > that case and stuck with 128 - 2.
> > > So, should we, instead, leave the default 128 - 2, for seg_max?
> > Argh!  Good point :-).
> > 
> > How about a seg_max_default property that is initialized to 254 for
> > modern machines and 126 to old machines?
> Hmm, but we'll achieve the same but with more code changes, don't we?
> 254 is because the queue-size is 256. We gonna leave 128-2 for older machine
> types
> just for not breaking anything. All other seg_max adjustment is provided by
> seg_max_adjust which is "on" by default in modern machine types.
> 
> to summarize:
> 
> modern mt defaults:
> seg_max_adjust = on
> queue_size = 256
> 
> => default seg_max = 254
> => changing queue-size will change seg_max = queue_size - 2
> 
> old mt defaults:
> seg_max_adjust = off
> queue_size = 128
> 
> => default seg_max = 126
> => changing queue-size won't change seg_max, it's always = 126 like it was
> before

You're right!  The only strange case is a modern machine type with
seg_max_adjust=off, where queue_size will be 256 but seg_max will be
126.  But no user would want to disable seg_max_adjust, so it's okay.

I agree with you that the line of code can remain unchanged:

  /*
   * Only old machine types use seg_max_adjust=off and there the default
   * value of queue_size is 128.
   */
  virtio_stl_p(vdev, &blkcfg.seg_max,
               s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);

Stefan

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Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

On 13.02.2020 12:08, Stefan Hajnoczi wrote:
> On Thu, Feb 13, 2020 at 11:08:35AM +0300, Denis Plotnikov wrote:
>> On 12.02.2020 18:43, Stefan Hajnoczi wrote:
>>> On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
>>>> The goal is to reduce the amount of requests issued by a guest on
>>>> 1M reads/writes. This rises the performance up to 4% on that kind of
>>>> disk access pattern.
>>>>
>>>> The maximum chunk size to be used for the guest disk accessing is
>>>> limited with seg_max parameter, which represents the max amount of
>>>> pices in the scatter-geather list in one guest disk request.
>>>>
>>>> Since seg_max is virqueue_size dependent, increasing the virtqueue
>>>> size increases seg_max, which, in turn, increases the maximum size
>>>> of data to be read/write from a guest disk.
>>>>
>>>> More details in the original problem statment:
>>>> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
>>>>
>>>> Suggested-by: Denis V. Lunev <den@openvz.org>
>>>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>>>> ---
>>>>    hw/block/virtio-blk.c | 4 ++--
>>>>    hw/core/machine.c     | 2 ++
>>>>    hw/scsi/virtio-scsi.c | 4 ++--
>>>>    3 files changed, 6 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>>>> index 09f46ed85f..6df3a7a6df 100644
>>>> --- a/hw/block/virtio-blk.c
>>>> +++ b/hw/block/virtio-blk.c
>>>> @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>>>        memset(&blkcfg, 0, sizeof(blkcfg));
>>>>        virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>>>        virtio_stl_p(vdev, &blkcfg.seg_max,
>>>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>>>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
>>> This value must not change on older machine types.
>> Yes, that's true, but ..
>>> So does this patch
>>> need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
>>> types get 126 instead of 254?
>> If we set seg-max-adjust "on" in older machine types, the setups using them
>> and having queue_sizes set , for example, 1024 will also set seg_max to 1024
>> - 2 which isn't the expected behavior: older mt didn't change seg_max in
>> that case and stuck with 128 - 2.
>> So, should we, instead, leave the default 128 - 2, for seg_max?
> Argh!  Good point :-).
>
> How about a seg_max_default property that is initialized to 254 for
> modern machines and 126 to old machines?
Hmm, but we'll achieve the same but with more code changes, don't we?
254 is because the queue-size is 256. We gonna leave 128-2 for older 
machine types
just for not breaking anything. All other seg_max adjustment is provided 
by seg_max_adjust which is "on" by default in modern machine types.

to summarize:

modern mt defaults:
seg_max_adjust = on
queue_size = 256

=> default seg_max = 254
=> changing queue-size will change seg_max = queue_size - 2

old mt defaults:
seg_max_adjust = off
queue_size = 128

=> default seg_max = 126
=> changing queue-size won't change seg_max, it's always = 126 like it 
was before

Denis
>
> Stefan

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Stefan Hajnoczi]

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On Thu, Feb 13, 2020 at 11:08:35AM +0300, Denis Plotnikov wrote:
> On 12.02.2020 18:43, Stefan Hajnoczi wrote:
> > On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
> > > The goal is to reduce the amount of requests issued by a guest on
> > > 1M reads/writes. This rises the performance up to 4% on that kind of
> > > disk access pattern.
> > > 
> > > The maximum chunk size to be used for the guest disk accessing is
> > > limited with seg_max parameter, which represents the max amount of
> > > pices in the scatter-geather list in one guest disk request.
> > > 
> > > Since seg_max is virqueue_size dependent, increasing the virtqueue
> > > size increases seg_max, which, in turn, increases the maximum size
> > > of data to be read/write from a guest disk.
> > > 
> > > More details in the original problem statment:
> > > https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> > > 
> > > Suggested-by: Denis V. Lunev <den@openvz.org>
> > > Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> > > ---
> > >   hw/block/virtio-blk.c | 4 ++--
> > >   hw/core/machine.c     | 2 ++
> > >   hw/scsi/virtio-scsi.c | 4 ++--
> > >   3 files changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > > index 09f46ed85f..6df3a7a6df 100644
> > > --- a/hw/block/virtio-blk.c
> > > +++ b/hw/block/virtio-blk.c
> > > @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
> > >       memset(&blkcfg, 0, sizeof(blkcfg));
> > >       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
> > >       virtio_stl_p(vdev, &blkcfg.seg_max,
> > > -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> > > +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
> > This value must not change on older machine types.
> Yes, that's true, but ..
> > So does this patch
> > need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
> > types get 126 instead of 254?
> If we set seg-max-adjust "on" in older machine types, the setups using them
> and having queue_sizes set , for example, 1024 will also set seg_max to 1024
> - 2 which isn't the expected behavior: older mt didn't change seg_max in
> that case and stuck with 128 - 2.
> So, should we, instead, leave the default 128 - 2, for seg_max?

Argh!  Good point :-).

How about a seg_max_default property that is initialized to 254 for
modern machines and 126 to old machines?

Stefan

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Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

On 12.02.2020 18:43, Stefan Hajnoczi wrote:
> On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
>> The goal is to reduce the amount of requests issued by a guest on
>> 1M reads/writes. This rises the performance up to 4% on that kind of
>> disk access pattern.
>>
>> The maximum chunk size to be used for the guest disk accessing is
>> limited with seg_max parameter, which represents the max amount of
>> pices in the scatter-geather list in one guest disk request.
>>
>> Since seg_max is virqueue_size dependent, increasing the virtqueue
>> size increases seg_max, which, in turn, increases the maximum size
>> of data to be read/write from a guest disk.
>>
>> More details in the original problem statment:
>> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
>>
>> Suggested-by: Denis V. Lunev <den@openvz.org>
>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>> ---
>>   hw/block/virtio-blk.c | 4 ++--
>>   hw/core/machine.c     | 2 ++
>>   hw/scsi/virtio-scsi.c | 4 ++--
>>   3 files changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>> index 09f46ed85f..6df3a7a6df 100644
>> --- a/hw/block/virtio-blk.c
>> +++ b/hw/block/virtio-blk.c
>> @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>>       memset(&blkcfg, 0, sizeof(blkcfg));
>>       virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>>       virtio_stl_p(vdev, &blkcfg.seg_max,
>> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
>> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
> This value must not change on older machine types.
Yes, that's true, but ..
> So does this patch
> need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
> types get 126 instead of 254?
If we set seg-max-adjust "on" in older machine types, the setups using 
them and having queue_sizes set , for example, 1024 will also set 
seg_max to 1024 - 2 which isn't the expected behavior: older mt didn't 
change seg_max in that case and stuck with 128 - 2.
So, should we, instead, leave the default 128 - 2, for seg_max?

Denis
>
>>       virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>>       virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>>       virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
>> @@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
>>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>>                       true),
>>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
>> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
>> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
>>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>>                        IOThread *),
>> diff --git a/hw/core/machine.c b/hw/core/machine.c
>> index 2501b540ec..3427d6cf4c 100644
>> --- a/hw/core/machine.c
>> +++ b/hw/core/machine.c
>> @@ -28,6 +28,8 @@
>>   #include "hw/mem/nvdimm.h"
>>   
>>   GlobalProperty hw_compat_4_2[] = {
>> +    { "virtio-blk-device", "queue-size", "128"},
>> +    { "virtio-scsi-device", "virtqueue_size", "128"},
>>       { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
>>       { "virtio-blk-device", "seg-max-adjust", "off"},
>>       { "virtio-scsi-device", "seg_max_adjust", "off"},
>> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
>> index 3b61563609..b38f50a429 100644
>> --- a/hw/scsi/virtio-scsi.c
>> +++ b/hw/scsi/virtio-scsi.c
>> @@ -660,7 +660,7 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>>   
>>       virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>>       virtio_stl_p(vdev, &scsiconf->seg_max,
>> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
>> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 256 - 2);
>>       virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>>       virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>>       virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
>> @@ -965,7 +965,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>>   static Property virtio_scsi_properties[] = {
>>       DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>>       DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
>> -                                         parent_obj.conf.virtqueue_size, 128),
>> +                                         parent_obj.conf.virtqueue_size, 256),
>>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>>                         parent_obj.conf.seg_max_adjust, true),
>>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>> -- 
>> 2.17.0
>>
>>

Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Stefan Hajnoczi]

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On Tue, Feb 11, 2020 at 05:14:14PM +0300, Denis Plotnikov wrote:
> The goal is to reduce the amount of requests issued by a guest on
> 1M reads/writes. This rises the performance up to 4% on that kind of
> disk access pattern.
> 
> The maximum chunk size to be used for the guest disk accessing is
> limited with seg_max parameter, which represents the max amount of
> pices in the scatter-geather list in one guest disk request.
> 
> Since seg_max is virqueue_size dependent, increasing the virtqueue
> size increases seg_max, which, in turn, increases the maximum size
> of data to be read/write from a guest disk.
> 
> More details in the original problem statment:
> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> 
> Suggested-by: Denis V. Lunev <den@openvz.org>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>  hw/block/virtio-blk.c | 4 ++--
>  hw/core/machine.c     | 2 ++
>  hw/scsi/virtio-scsi.c | 4 ++--
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..6df3a7a6df 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>      memset(&blkcfg, 0, sizeof(blkcfg));
>      virtio_stq_p(vdev, &blkcfg.capacity, capacity);
>      virtio_stl_p(vdev, &blkcfg.seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);

This value must not change on older machine types.  So does this patch
need to turn seg-max-adjust *on* in hw_compat_4_2 so that old machine
types get 126 instead of 254?

>      virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
>      virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
>      virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
> @@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
>      DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                      true),
>      DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
>      DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>      DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                       IOThread *),
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2501b540ec..3427d6cf4c 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -28,6 +28,8 @@
>  #include "hw/mem/nvdimm.h"
>  
>  GlobalProperty hw_compat_4_2[] = {
> +    { "virtio-blk-device", "queue-size", "128"},
> +    { "virtio-scsi-device", "virtqueue_size", "128"},
>      { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
>      { "virtio-blk-device", "seg-max-adjust", "off"},
>      { "virtio-scsi-device", "seg_max_adjust", "off"},
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..b38f50a429 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -660,7 +660,7 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
>  
>      virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
>      virtio_stl_p(vdev, &scsiconf->seg_max,
> -                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
> +                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 256 - 2);
>      virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
>      virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
>      virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
> @@ -965,7 +965,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>  static Property virtio_scsi_properties[] = {
>      DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
>      DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> -                                         parent_obj.conf.virtqueue_size, 128),
> +                                         parent_obj.conf.virtqueue_size, 256),
>      DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                        parent_obj.conf.seg_max_adjust, true),
>      DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
> -- 
> 2.17.0
> 
> 

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[PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Denis Plotnikov]

The goal is to reduce the amount of requests issued by a guest on
1M reads/writes. This rises the performance up to 4% on that kind of
disk access pattern.

The maximum chunk size to be used for the guest disk accessing is
limited with seg_max parameter, which represents the max amount of
pices in the scatter-geather list in one guest disk request.

Since seg_max is virqueue_size dependent, increasing the virtqueue
size increases seg_max, which, in turn, increases the maximum size
of data to be read/write from a guest disk.

More details in the original problem statment:
https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html

Suggested-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 hw/block/virtio-blk.c | 4 ++--
 hw/core/machine.c     | 2 ++
 hw/scsi/virtio-scsi.c | 4 ++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 09f46ed85f..6df3a7a6df 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -914,7 +914,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
     memset(&blkcfg, 0, sizeof(blkcfg));
     virtio_stq_p(vdev, &blkcfg.capacity, capacity);
     virtio_stl_p(vdev, &blkcfg.seg_max,
-                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
+                 s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 256 - 2);
     virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
     virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
     virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size);
@@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
     DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
                     true),
     DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
-    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
+    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
     DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
     DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
                      IOThread *),
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 2501b540ec..3427d6cf4c 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -28,6 +28,8 @@
 #include "hw/mem/nvdimm.h"
 
 GlobalProperty hw_compat_4_2[] = {
+    { "virtio-blk-device", "queue-size", "128"},
+    { "virtio-scsi-device", "virtqueue_size", "128"},
     { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
     { "virtio-blk-device", "seg-max-adjust", "off"},
     { "virtio-scsi-device", "seg_max_adjust", "off"},
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 3b61563609..b38f50a429 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -660,7 +660,7 @@ static void virtio_scsi_get_config(VirtIODevice *vdev,
 
     virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues);
     virtio_stl_p(vdev, &scsiconf->seg_max,
-                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2);
+                 s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 256 - 2);
     virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors);
     virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun);
     virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
@@ -965,7 +965,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
 static Property virtio_scsi_properties[] = {
     DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1),
     DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
-                                         parent_obj.conf.virtqueue_size, 128),
+                                         parent_obj.conf.virtqueue_size, 256),
     DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
                       parent_obj.conf.seg_max_adjust, true),
     DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
-- 
2.17.0