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Re: [Qemu-devel] [PATCH v1] ppc: Force CPU threads count to be a power o
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From: |
Bharata B Rao |
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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: |
Wed, 5 Mar 2014 12:09:19 +0530 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Mar 04, 2014 at 09:13:38PM -0700, Eric Blake wrote:
> 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.
Nice. Using is_power_of_2() in v2.
Regards,
Bharata.