Re: [PATCH] kvm: Increase NR_IOBUS_DEVS limit to 200

2010-04-01 Thread Avi Kivity 

On 03/31/2010 02:48 AM, Sridhar Samudrala wrote:

This patch increases the current hardcoded limit of NR_IOBUS_DEVS
from 6 to 200. We are hitting this limit when creating a guest with more
than 1 virtio-net device using vhost-net backend. Each virtio-net
device requires 2 such devices to service notifications from rx/tx queues.
   


Applied, thanks.

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error compiling committee.c: too many arguments to function

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Re: [PATCH] kvm: Increase NR_IOBUS_DEVS limit to 200

2010-03-31 Thread Michael S. Tsirkin 
On Tue, Mar 30, 2010 at 04:48:25PM -0700, Sridhar Samudrala wrote:
 This patch increases the current hardcoded limit of NR_IOBUS_DEVS
 from 6 to 200. We are hitting this limit when creating a guest with more
 than 1 virtio-net device using vhost-net backend. Each virtio-net
 device requires 2 such devices to service notifications from rx/tx queues.
 
 Signed-off-by: Sridhar Samudrala s...@us.ibm.com
 

I tried this, but observed a measurable performance
degradation with vhost net and this patch. Did not
investigate yet.  Do you see this as well?

 diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
 index a3fd0f9..7fb48d3 100644
 --- a/include/linux/kvm_host.h
 +++ b/include/linux/kvm_host.h
 @@ -54,7 +54,7 @@ extern struct kmem_cache *kvm_vcpu_cache;
   */
  struct kvm_io_bus {
   int   dev_count;
 -#define NR_IOBUS_DEVS 6
 +#define NR_IOBUS_DEVS 200 
   struct kvm_io_device *devs[NR_IOBUS_DEVS];
  };
  
 
 
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Re: [PATCH] kvm: Increase NR_IOBUS_DEVS limit to 200

2010-03-31 Thread Sridhar Samudrala 
On Wed, 2010-03-31 at 12:51 +0300, Michael S. Tsirkin wrote:
 On Tue, Mar 30, 2010 at 04:48:25PM -0700, Sridhar Samudrala wrote:
  This patch increases the current hardcoded limit of NR_IOBUS_DEVS
  from 6 to 200. We are hitting this limit when creating a guest with more
  than 1 virtio-net device using vhost-net backend. Each virtio-net
  device requires 2 such devices to service notifications from rx/tx queues.
  
  Signed-off-by: Sridhar Samudrala s...@us.ibm.com
  
 
 I tried this, but observed a measurable performance
 degradation with vhost net and this patch. Did not
 investigate yet.  Do you see this as well?

No. I am not seeing any degradation that is not within the range of
variation seen with kvm networking.
For ex: On a Nehalem 2 socket, 8 core system, running netperf TCP_STREAM
with 64K size packets, i am getting 12-13Gb/s guest to host and
11-12Gb/s host to guest with and without this patch.

Thanks
Sridhar


 
  diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
  index a3fd0f9..7fb48d3 100644
  --- a/include/linux/kvm_host.h
  +++ b/include/linux/kvm_host.h
  @@ -54,7 +54,7 @@ extern struct kmem_cache *kvm_vcpu_cache;
*/
   struct kvm_io_bus {
  int   dev_count;
  -#define NR_IOBUS_DEVS 6
  +#define NR_IOBUS_DEVS 200 
  struct kvm_io_device *devs[NR_IOBUS_DEVS];
   };
   
  
  

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[PATCH] kvm: Increase NR_IOBUS_DEVS limit to 200

2010-03-30 Thread Sridhar Samudrala 
This patch increases the current hardcoded limit of NR_IOBUS_DEVS
from 6 to 200. We are hitting this limit when creating a guest with more
than 1 virtio-net device using vhost-net backend. Each virtio-net
device requires 2 such devices to service notifications from rx/tx queues.

Signed-off-by: Sridhar Samudrala s...@us.ibm.com


diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a3fd0f9..7fb48d3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -54,7 +54,7 @@ extern struct kmem_cache *kvm_vcpu_cache;
  */
 struct kvm_io_bus {
int   dev_count;
-#define NR_IOBUS_DEVS 6
+#define NR_IOBUS_DEVS 200 
struct kvm_io_device *devs[NR_IOBUS_DEVS];
 };
 



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