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RE: [Xen-devel] [PATCH] Fix the very-slow-IDE-IO-speed issue of Qemu0.90

To: "Cui, Dexuan" <dexuan.cui@xxxxxxxxx>, "xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] Fix the very-slow-IDE-IO-speed issue of Qemu0.90
From: "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 29 May 2007 06:25:40 +0100
Delivery-date: Mon, 28 May 2007 22:25:08 -0700
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Thread-topic: [Xen-devel] [PATCH] Fix the very-slow-IDE-IO-speed issue of Qemu0.90
> c/s 15021 updated Qemu to 0.90. In the new Qemu's ide.c, asynchronous
> (AIO) is used to replace the previous DMA thread; here when an AIO
> request is completed, dom0 sends a signal SIGUSR2 to Qemu (see
> block-raw.c: qemu_aio_init(),raw_aio_setup()), then the signal
> interrupts the select() in main_loop_wait() at once, next,
> qemu_aio_poll() is called to reap a completed AIO request.
> However, in certain Linux distributions (i.e., x86_64 RHEL 4u4), if
> Qemu is spawned by the python script image.py of Control Panel, the
> of Qemu is blocked by default due to some reasons 

Good work figuring this out! It perfectly explains why most folk weren't
seeing the problem.

Have you got any comparative performance numbers comparing IDE
performance before and after the 0.90 upgrade (with your fix)? Are we
back to roughly where we were?


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