Messages in this thread |  | | Date | Sat, 14 Oct 2000 14:20:41 -0400 (EDT) | From | Eric Lowe <> | Subject | Re: mapping user space buffer to kernel address space |
| |
Hello,
> Note that it is usually MUCH better to do this the other way around: > having a kernel-side buffer, and mapping that into user space. I don't > understand why so many people always want to do it the wrong way around..
Well, I totally agree. Unfortunately, my fellow driver developers seem to think "because it's in UNIX" means "it must be a good idea". Pinning pages in memory leaves big holes in processes that can't be swapped out on systems that really need the VM to be able to work its magic under load.
Fortunately, VIA and similar schemes try to address the problem in the application, OS, _and_ hardware simultaneously.. In the future we will probably tell our customers (Fibre Channel) that if they really want good performance, they need to use VI instead of IP, and to avoid such hacks as pinning user pages for proprietary protocols.. My experience has been that systems that do a lot of page pinning in UNIX for I/O don't gain much in performance anyway, but it _really_ puts a lot of stress on the system compared to doing it the right way.
-- Eric Lowe Software Engineer, Systran Corporation elowe@systran.com
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
|  |