Messages in this thread | | | Subject | Re: [RFC] block layer support for DMA IOMMU bypass mode II | From | James Bottomley <> | Date | 30 Jul 2003 12:18:46 -0500 |
| |
On Wed, 2003-07-30 at 11:36, Andi Kleen wrote: > The differences were greater with the mpt fusion driver, maybe it has > more overhead. Or your IO subsystem is significantly different.
By and large, these results are more like what I expect.
As I've said before, getting SG tables to work efficiently is a core part of getting an I/O board to function.
There are two places vmerging can help:
1. Reducing the size of the SG table 2. Increasing the length of the I/O for devices with fixed (but small) SG table lengths.
However, it's important to remember that vmerging comes virtually for free in the BIO layer, so the only added cost is the programming of the IOMMU. This isn't an issue on SPARC, PA-RISC and the like where IOMMU programming is required to do I/O, it may be something the IOMMU optional architectures (like IA-64 and AMD-64) should consider, which is where I entered with the IOMMU bypass patch.
James
- 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/
| |