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Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure |
Date: |
Tue, 6 Oct 2015 13:49:50 +0100 |
On 5 October 2015 at 15:27, Paolo Bonzini <address@hidden> wrote:
> I remember seeing a bug where this terrible implementation caused
> divisions by zero on the host. The default implementation in
> include/qemu/timer.h should be changed to
> qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL).
>
> Note that in practice this terrible implementation is only used on
> ARM/AArch64. Is PMCCNTR or something similar accessible from userspace?
> I guess no, since even write access is enabled via PMUSERENR (and in
> general PMUSERENR ought to be false on a preemptive-multitasking OS).
Yeah, there's no guarantee on userspace access. I think the
fastest way to get some kind of count is to use a library
function that boils down to gettimeofday(2), which we will
do purely in userspace in the kernel VDSO if possible.
thanks
-- PMM
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, (continued)
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Christopher Covington, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Peter Crosthwaite, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Christopher Covington, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Peter Maydell, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Paolo Bonzini, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Peter Maydell, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Paolo Bonzini, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure,
Peter Maydell <=
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Paolo Bonzini, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Peter Maydell, 2015/10/08
- Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure, Paolo Bonzini, 2015/10/08