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Re: [Xen-devel] atomic counters larger than 24 bits?
| To: | Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> |
|---|---|
| Subject: | Re: [Xen-devel] atomic counters larger than 24 bits? |
| From: | Keir Fraser <keir.fraser@xxxxxxxxxxxxx> |
| Date: | Fri, 27 Mar 2009 08:52:44 +0000 |
| Cc: | "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx> |
| Delivery-date: | Fri, 27 Mar 2009 01:54:41 -0700 |
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| Thread-topic: | [Xen-devel] atomic counters larger than 24 bits? |
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On 26/03/2009 23:26, "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxx> wrote: > Dan Magenheimer, le Thu 26 Mar 2009 19:38:13 +0000, a écrit : >> In tmem, I have some counters that I need to keep coherent, >> preferably without a lock, so I'm using atomic_inc/dec etc. >> However the comments in include/asm-x86/atomic.h say repeatedly >> that the "useful range of an atomic_t is only 24 bits". > > IIRC the historical reason for this is that some Linux architectures > weren't providing more. The x86 implementation does support signed 32 > bits. I believe the ia64 implementation does too. Yes, I'll fix the x86/atomic.h comments. Our atomic_t type is signed and at least 32 bits. I don't see we'll ever port to an architecture without cmpxchg or similar to easily support 'full width' atomic_t. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel |
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