From: Bharata B Rao <bharata@linux.vnet.ibm.com>
To: Eric Blake <eblake@redhat.com>
Cc: aik@ozlabs.ru, stewart@linux.vnet.ibm.com, qemu-devel@nongnu.org,
agraf@suse.de
Subject: Re: [Qemu-devel] [PATCH v1] ppc: Force CPU threads count to be a power of 2.
Date: Wed, 5 Mar 2014 12:09:19 +0530 [thread overview]
Message-ID: <20140305063919.GE20295@in.ibm.com> (raw)
In-Reply-To: <5316A472.6030402@redhat.com>
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.
prev parent reply other threads:[~2014-03-05 6:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-05 3:36 [Qemu-devel] [PATCH v1] ppc: Force CPU threads count to be a power of 2 Bharata B Rao
2014-03-05 4:13 ` Eric Blake
2014-03-05 6:39 ` Bharata B Rao [this message]
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