Xen devel - Oct 2009 - doubt regarding IO scheduler and credit scheduling in netback

Hi,
With reference to the netback and netfront model of device driver in
Xen(specifically Xen 3.1.3 and linux 2.6.18.8-- I know it is a bit old but
please excuse), I am confused as to where the network IO scheduler fits in.
I have read that there are different types of IO schedulers in linux -
deadline ,anticipatory, complete fair queueing (cfq )etc. where cfq is the
default. Is it only being used in the context of disk IO? or the same thing
is used for network IO?

Also (as a related doubt), in netback code(In netback.c net_tx_action ) , I
saw some credit scheduling of the network interfaces(netif_t *netif)
corresponding to guest domains. So whenever Dom 0 is scheduled ,it does a
credit scheduling of the network interfaces corresponding to different
DomUs. The credits will get refreshed when the credit_timeout happens. The
next network interface(netif) will be scheduled if the credits for the
current netif is exhausted. Is my understanding correct ?
What are the other cases when the next netif is scheduled? (one would
obviously be the case when there are no packets to send. Any other case?)
When I did some experiments, I found that the bandwidth is fairly divided
among all the domains. So there should be some mechasim to ensure this.

In this context where does the IO scheduler fits in?
Please explain.

Thanks
Kuriakose Mathew


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Just to clarify , hope the above credit scheduling has nothing to do with
the cpu credit scheduling at the hypervisor?


On Fri, Oct 23, 2009 at 8:46 AM, Kuriakose Mathew
<kmathew123@gmail.com>wrote:
> Hi,
> With reference to the netback and netfront model of device driver in
> Xen(specifically Xen 3.1.3 and linux 2.6.18.8-- I know it is a bit old but
> please excuse), I am confused as to where the network IO scheduler fits in.
> I have read that there are different types of IO schedulers in linux -
> deadline ,anticipatory, complete fair queueing (cfq )etc. where cfq is the
> default. Is it only being used in the context of disk IO? or the same thing
> is used for network IO?
>
> Also (as a related doubt), in netback code(In netback.c net_tx_action ) , I
> saw some credit scheduling of the network interfaces(netif_t *netif)
> corresponding to guest domains. So whenever Dom 0 is scheduled ,it does a
> credit scheduling of the network interfaces corresponding to different
> DomUs. The credits will get refreshed when the credit_timeout happens. The
> next network interface(netif) will be scheduled if the credits for the
> current netif is exhausted. Is my understanding correct ?
> What are the other cases when the next netif is scheduled? (one would
> obviously be the case when there are no packets to send. Any other case?)
> When I did some experiments, I found that the bandwidth is fairly divided
> among all the domains. So there should be some mechasim to ensure this.
>
> In this context where does the IO scheduler fits in?
> Please explain.
>
> Thanks
> Kuriakose Mathew
>
>

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Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

I ll put my question differently.

I have read that there are different types of IO schedulers in linux -
deadline ,anticipatory, complete fair queueing (cfq )etc. where cfq is the
default. Is it only being used in the context of disk IO? or the same thing
is used for network IO? When does this get called with respect to xen
frontend-backend drivers .

Please explain.


On Fri, Oct 23, 2009 at 9:20 AM, Kuriakose Mathew
<kmathew123@gmail.com>wrote:
> Just to clarify , hope the above credit scheduling has nothing to do with
> the cpu credit scheduling at the hypervisor?
>
>
>
> On Fri, Oct 23, 2009 at 8:46 AM, Kuriakose Mathew
<kmathew123@gmail.com>wrote:
>
>> Hi,
>> With reference to the netback and netfront model of device driver in
>> Xen(specifically Xen 3.1.3 and linux 2.6.18.8-- I know it is a bit old
but
>> please excuse), I am confused as to where the network IO scheduler fits
in.
>> I have read that there are different types of IO schedulers in linux -
>> deadline ,anticipatory, complete fair queueing (cfq )etc. where cfq is
the
>> default. Is it only being used in the context of disk IO? or the same
thing
>> is used for network IO?
>>
>> Also (as a related doubt), in netback code(In netback.c net_tx_action )
,
>> I saw some credit scheduling of the network interfaces(netif_t *netif)
>> corresponding to guest domains. So whenever Dom 0 is scheduled ,it does
a
>> credit scheduling of the network interfaces corresponding to different
>> DomUs. The credits will get refreshed when the credit_timeout happens.
The
>> next network interface(netif) will be scheduled if the credits for the
>> current netif is exhausted. Is my understanding correct ?
>> What are the other cases when the next netif is scheduled? (one would
>> obviously be the case when there are no packets to send. Any other
case?)
>> When I did some experiments, I found that the bandwidth is fairly
divided
>> among all the domains. So there should be some mechasim to ensure this.
>>
>> In this context where does the IO scheduler fits in?
>> Please explain.
>>
>> Thanks
>> Kuriakose Mathew
>>
>>
>

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