Re: [Xen-devel] Dom0 physical networking/swiotlb/something issue in 3.7-rc1

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.11.12 at 10:16, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Fri, 2012-11-09 at 09:03 +0000, Jan Beulich wrote:
>> >>> On 12.10.12 at 12:28, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
>> > The following patch causes fairly large packet loss when transmitting
>> > from dom0 to the physical network, at least with my tg3 hardware, but I
>> > assume it can impact anything which uses this interface.
>> > 
>> > I suspect that the issue is that the compound pages allocated in this
>> > way are not backed by contiguous mfns and so things fall apart when the
>> > driver tries to do DMA.
>> 
>> Has this seen any sort of resolution yet? Despite having forced
>> NETDEV_FRAG_PAGE_MAX_ORDER to zero for Xen (following
>> your suggested patch, Ian), and with a different NIC (e1000e
>> driven) I'm seeing similar packet loss/corruption on transmits,
>> and only if running a debug hypervisor (in a non-debug one,
>> MFNs are largely contiguous, so this issue should be observable
>> there only very rarely).
> 
> I think Konrad is still looking into the underlying swiotlb issue.
> 
> If you want to go with the workaround then there is another order>0 to
> frob in net/core/sock.c
> #define SKB_FRAG_PAGE_ORDER   get_order(32768)
> which might help.

Thanks, that indeed helped. And gives me food for thought as
well, since this should - if anything at all - be a performance
improvement, not a something affecting correctness.

Jan


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