On 2012-Jul-03 21:17:53 +1000, Peter Jeremy <[email protected]> wrote: >I have a reasonably recent 8-stable/amd64 system (r237444) with a "ATI >Radeon HD 2400 Pro", xorg-server-1.10.6,1 and xf86-video-ati-6.14.3_1 >8GB RAM and ZFS. I'm seeing fairly consistent problems with Xorg ... >How difficult would it be to modify bus_dmamem_alloc() [at least on >x86] to handle multi-segment allocations?
I think I've managed to create an amd64 bus_dmamem_alloc() that allows page-sized allocations as long as no boundary condition is specified and no more than page-sized alignment is required (porting it to other architectures would be trivial). I've given it a quick whirl inside a VBox and no smoke came out but I'd appreciate someone with a better understanding of bus_dma(9) and vm/vm_contig.c giving http://www.rulingia.com/bugs/patch-wiredmalloc a once-over. Note that this patch is against 8.x but there's only a trivial difference to head. BTW, the comment in busdma_machdep.c:bus_dmamem_alloc() * XXX Use Contigmalloc until it is merged into this facility * and handles multi-seg allocations. Nobody is doing * multi-seg allocations yet though. * XXX Certain AGP hardware does. does not appear to be accurate. Apart from drm, quite a few drivers call bus_dma_tag_create(9) with multiple segments and also call bus_dmamem_alloc(9) [though I haven't verified that the calls share the same bus_dma_tag, so I can't be absolutely certain]. BTW(2): Whilst studying busdma_machdep.c for arm and mips, I've noticed they appear to potentially allocate substantial kernel stack under some conditions as several bus_dma(9) functions include: bus_dma_segment_t dm_segments[dmat->nsegments]; What prevents this overflowing the kernel stack? -- Peter Jeremy
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