Re: [TUHS] UNIX on S/370

On Nov 20, 2017 8:51 PM, "Larry McVoy" <lm(a)mcvoy.com> wrote: Actually, how common was that? I know at SGI we did that with O_DIRECT on files (and just automatically on the way for in networking and page flipped on the way out). But it was a pile of work, you had to lock all the pages so that the pageout daemon didn't page them out, etc. So under what circumstances would Unix do DMA to/from user buffers rather than bcopy it? I assume you aren't talking about things like mmap where you can't really bcopy it... At Fusion I/O we had hooks into our PCIe flash card driver that would do DMA directly into user buffers (since we wanted IOPS and any extra copies got in the way of that). We also played fun tricks with 'extended I/O primitives' that were implemented with ioctls, but still did I/O to/from user buffers. This was so we could construct 1 transaction for what's basically an atomic writev (more complicated than that, because the atomic operation also supported delete/trim operations at the same time). This was to simplify checkpointing since it was an all or nothing thing: if we couldn't do it, or the system crashed in the middle, the transaction never happened. There were other, more extended I/O operations that involved read as well that were kinda crazy, but useful for a market segment we did well in. Also likely no the sort of thing that you were thinking about, but it was a novel use of DMA to user buffers. Warner On Mon, Nov 20, 2017 at 10:15:58PM -0500, Ron Natalie wrote: put be -- --- Larry McVoy lm at mcvoy.com http://www.mcvoy.com/lm