Re: [MirageOS-devel] wireshark capture of failed download from mirage-www on ARM

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 22 Jul 2014, at 02:01, Thomas Leonard <talex5@xxxxxxxxx> wrote:

> On 22 July 2014 09:14, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>> On 22 Jul 2014, at 01:10, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>> 
>>> I noticed I'm getting a lot of these in the dom0 log (dmsg):
>>> 
>>> Jul 22 08:09:05 cubietruck kernel: [11892.128241]
>>> xen_add_phys_to_mach_entry: cannot add pfn=0x00079abe ->
>>> mfn=0x000bed87: pfn=0x000799a6 -> mfn=0x000bed87 already exists
>>> Jul 22 08:09:05 cubietruck kernel: [11892.128727]
>>> xen_add_mach_to_phys_entry: cannot add pfn=0x00079bcb ->
>>> mfn=0x000bed87: pfn=0x000799a6 -> mfn=0x000bed87 already exists
>>> Jul 22 08:09:05 cubietruck kernel: [11892.133264]
>>> xen_add_phys_to_mach_entry: cannot add pfn=0x00079b70 ->
>>> mfn=0x000bed87: pfn=0x00079bd7 -> mfn=0x000bed87 already exists
>>> Jul 22 08:09:09 cubietruck kernel: [11896.041106]
>>> xen_add_phys_to_mach_entry: cannot add pfn=0x0007999a ->
>>> mfn=0x000bed87: pfn=0x00079b2b -> mfn=0x000bed87 already exists
>> 
>> That looks like this bug in Xen/ARM/netback:
>> http://lists.xenproject.org/archives/html/xen-users/2014-07/msg00067.html
> 
> Aha! This seems to fix it (I can browse mirage-www without huge delays):
> 
> diff --git a/lib/netif.ml b/lib/netif.ml
> index 4e02e5e..3cc7760 100644
> --- a/lib/netif.ml
> +++ b/lib/netif.ml
> @@ -455,7 +455,7 @@ let writev nf pages =
>          lwt rest_th = xmit other_pages in
>          (* All fragments are now written, we can now notify the backend *)
>          Lwt_ring.Front.push nf.t.tx_client (notify nf.t);
> -         return ()
> +         join rest_th
>     )
> 
> let wait_for_plug nf =
> 
> Not very efficient, but at least it works! Looks like the Xen people
> will fix it at some point.

That's going to serialize requests on the TX ring, isn't it?  Might
be worth making conditional via a feature flag if it's going to take
x86 transmit performance down.

-anil

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