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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O |
Date: | Mon, 03 Dec 2007 15:36:42 -0600 |
User-agent: | Thunderbird 2.0.0.6 (X11/20071022) |
Paul Brook wrote:
Yes, librt is providing posix-aio, and librt coming with GNU libc uses threads. But if I remember correctly librt coming with RHEL uses a mix of threads and linux kernel AIO (you can have a look to the .srpm of libc). BTW, if everyone thinks it could be a good idea I can port block-raw.c to use linux kernel AIO (without removing POSIX AIO support, of course)This seems rather pointless, given a user can just use a linux-AIO librt instead.
Not at all. linux-aio is the only interface that allows you to do asynchronous fdsync which simulates a barrier which allows for an ordered queue.
I have a patch that uses linux-aio for the virtio-blk driver I'll be posting tomorrow and I'm extremely happy with the results. In recent kernels, you can use an eventfd interface along with linux-aio so that polling is unnecessary. Along with O_DIRECT and the preadv/pwritev interface, you can make a block backend in userspace that performs just as well as if it were in the kernel.
The posix-aio interface simply doesn't provide a mechanism to do these things.
Regards, Anthony Liguori
Paul
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