[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Dom0 physical networking/swiotlb/something issue in 3.7-rc1
>>> On 09.11.12 at 10:40, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: >>>> 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. Okay, one problem in the pv-ops case seems pretty obvious: dma_capable() does (potentially cross-page) arithmetic on a dma_addr_t value, ignoring dis-contiguity altogether. Specifically its first use in swiotlb_map_page() and its only use in swiotlb_map_sg_attrs() are problematic. In the forward ported kernels, those two checks are however accompanied by range_needs_mapping() (aka range_straddles_page_boundary()) checks, which ought to take care of this. There is brokenness there with the invocations of gnttab_dma_map_page(), but only if the initial offset is at least PAGE_SIZE - will have to check whether that occurs. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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