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[Qemu-devel] deterministic qemu
From: |
Steven Seeger |
Subject: |
[Qemu-devel] deterministic qemu |
Date: |
Wed, 31 Jan 2018 00:50:57 -0500 |
I wanted to update the list on my progress and a follow-up of the "ppc and
icount" thread.
The issue I was seeing is the case where an io memory write triggers a timer
value to be set. In single-thread TCG, timers are run in
handle_icount_deadline() and once that's done, TBs are executed. Since cpu-
>icount_budget is 5000000 (icount==3), a timer being set to 88 microseconds
will fire way late. This caused the tremendous slowdown I was seeing during
the start of my binary when the vxWorks bootup banner came up. I have a simple
fix for this (set cpu->exit_request=1 in qemu_start_warp_timer, a total hack)
but I'm sure that's not "correct."
The other thing is -icount 3,align=on makes it run correctly assuming the host
can keep up.
The end result is every time I run my executable I get the same virtual clock
value for some given event. I'm very happy.
I still don't have a fix for the issue in commit
044897ef4a22af89aecb8df509477beba0a2e0ce but I reverted it and things are
working for me.
Steven
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