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From: | Gerd Hoffmann |
Subject: | Re: [Qemu-devel] [PATCH 18/18] usb: add ehci adapter |
Date: | Tue, 17 May 2011 17:02:34 +0200 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110419 Red Hat/3.1.10-1.el6_0 Thunderbird/3.1.10 |
Hi,
(And by the way, where are the focused patches for each, especially the last one - nuking the 8kHz code?
It's squashed in, like everything else.
We know that it worked on linux and that printers, scanners and storage devices worked ok (mostly).
8 kHz is insane.I looked closely while trying to make 8 kHz a runtime option instead of a compile time option, then decided to drop it altogether as it is totally pointless. qemu simply can't handle that wakeup rate. It maxed out at ~3 kHz wakeups in my tests. And it burns tons of CPU time.
I also don't see what it would buy us. We can wakeup with 1 kHz rate (maybe even lower), then emulate 8 (or more) microframes each time.
Throughput issues (guess this is the reason to try 8kHz wakeups) need to be addressed by modeling data pipes in the usb system instead of playing ping-pong between EHCI and USB device emulation for each single usb packet, at 8 kHz.
I see the ehci merge just as very first step. USB 2.0 (and 3.0) support in qemu still has a loooooooong way to go.
cheers, Gerd
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