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Re: [Qemu-devel] [PATCH v1] ppc: Force CPU threads count to be a power o
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From: |
Eric Blake |
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Subject: |
Re: [Qemu-devel] [PATCH v1] ppc: Force CPU threads count to be a power of 2. |
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Date: |
Tue, 04 Mar 2014 21:13:38 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 |
On 03/04/2014 08:36 PM, Bharata B Rao wrote:
> PowerPC kernel expects the number of SMT threads in a core to be a power
> of 2. Since QEMU doesn't enforce this, it leads to an early guest kernel
> crash if invalid threads count is specified.
>
> Prevent this crash and make it a graceful exit from QEMU itself by
> validating the user supplied threads count.
>
>
> +#include <math.h>
> }
> + threads_shift = log2(smp_threads);
Overkill. qemu-common.h gives you is_power_of_2() that uses just
integer math rather than dragging in floating-point overhead of libm.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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