Messages in this thread | | | Subject | Re: how to bypass buffer cache for a block device driver | Date | Mon, 9 Aug 1999 15:52:34 +0100 (BST) | From | Alan Cox <> |
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> I want to optimize network related disk access by avoiding > buffer copies into the main RAM. (Nic card will directly pick up > data from storage controller card.)
Ok in which case you will definitely need to do a fair bit of kernel hacking.
> I do not want apps running on the host machine itself to get > adversely impacted.
Nod - but they want to share the page cache too so you need to run a distributed shared memory scheme between your NFS daemon, the kernel page cache and the card. Not fun
> I do not mind patching nfs server or writing device driver > but I do not want to patch the kernel as I finally want it > running on a stock kernel.
The NFS server (knfsd) is in the kernel
> How is the general problem of "peer-to-peer" access of hardware > addressed in linux? Is there a generic way hardware can pass > data bypassing copies to host memory.
Not currently. We do obvious stuff like video capture direct to the frame buffer. Disk I/O however is going via the page cache and we need to keep that coherent. Stephen Tweedie has done some initial work on raw userspace<->controller I/O for Linux that can handle raw I/O for raw disk partitions.
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