On Fri, 11 Jul 2008 06:52:09 -0400 (EDT) Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > On Fri, 11 Jul 2008, FUJITA Tomonori wrote: > > > On Thu, 10 Jul 2008 17:56:08 -0400 (EDT) > > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > >> When I thought about it more, I realized that this accounting of virtual > >> segments in I/O layer can't work correctly at all. If an architecture > >> defines symbols BIOVEC_VIRT_MERGEABLE and BIOVEC_VIRT_OVERSIZE, it > >> declares that it's IOMMU must merge any two regions satisfying these > >> conditions. But in an IOMMU, it is impossible to guarantee, because: > > > > Yeah, IOMMUs can't guarantee that. The majority of architectures set > > BIO_VMERGE_BOUNDARY to 0 so they don't hit this, I think. > > Yes, the architectures without IOMMU don't hit this problem. I meant that even if some architectures support IOMMUs, they set BIO_VMERGE_BOUNDARY to 0. > >> * the bus address is allocated basiclly randomly, so we can hit > >> dev->dma_parms->segment_boundary_mask any time. This will prevent virtual > >> merging from happenning. I/O layer doesn't know the bus address at the > >> time it merges requests, so it can't predict when this happens. > >> > >> * the IOMMU isn't guaranteed to find a continuous space in it's bus > >> address space. If it skips over already mapped regions, it can't perform > >> virtual merging. > >> > >> * when creating the mapping, we can hit per-device limit > >> "dev->dma_parms->max_segment_size" --- but the I/O layer checks only > >> against global limit BIOVEC_VIRT_OVERSIZE. (this last issue is fixable, > >> the previous two are not). > > > > I think that the block layer can handle this properly via > > q->max_segment_size. We have the same value at two different > > places. Yeah, it's not good... > > > > > > BTW, inia100_template sets sg_tablesize to SG_ALL. If the controller > > has at most 32 SG entries per request, we need to fix that. > > Later, it sets that to shost->sg_tablesize = TOTAL_SG_ENTRY; I don't know > why in inia100_template there is SG_ALL. Thanks, I overlooked it. Seems that the driver sets shost->sg_tablesize to TOTAL_SG_ENTRY unconditionally. Setting it in inia100_template is better. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
