lkml.org 
[lkml]   [2007]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Containment measures for slab objects on scatter gather lists
> DMA to or from memory should be done via the DMA mapping API.  If we're
> DMAing to/from a limited range within a page, either we should be using
> dma_map_single(), or dma_map_page() with an appropriate offset and size.

If those ranges overlap a cache line then the dma mapping API will not
save your backside.

On a system with a 32 byte cache granularity what happens if you get two
dma mapping calls for x and x+16. Right now the thing that avoids this
occurring is that the allocators don't pack stuff in that hard so x+16
always belongs to the same driver and we can hope driver authors are
sensible

> sizes, but they do happen. We handle this on ARM by writing back
> the overlapped lines and invalidating the rest before the DMA operation
> commences, and hope that the overlapped lines aren't touched for the
> duration of the DMA.)

The combination of "hope" and "DMA" isn't a good one for stable system
design. In this situation we should be waving large red flags
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-30 01:09    [from the cache]
©2003-2011 Jasper Spaans