From mboxrd@z Thu Jan  1 00:00:00 1970
From: compudj@krystal.dyndns.org (Mathieu Desnoyers)
Date: Thu, 18 Feb 2010 11:09:34 -0500
Subject: [ltt-dev] [PATCH 12/12] centralize definition of BITS_PER_LONG
In-Reply-To: <4B7D5C45.9020804@redhat.com>
References: <1266260686-17588-1-git-send-email-pbonzini@redhat.com>
	<1266260686-17588-13-git-send-email-pbonzini@redhat.com>
	<20100218032554.GG11338@Krystal> <4B7CFE10.8070803@redhat.com>
	<20100218134600.GA5825@Krystal> <4B7D5C45.9020804@redhat.com>
Message-ID: <20100218160934.GA17107@Krystal>

* Paolo Bonzini (pbonzini at redhat.com) wrote:
> On 02/18/2010 02:46 PM, Mathieu Desnoyers wrote:
>>> >
>>> >  I32LLP64 is basically only Mingw64 and ia64-hpux.
>> And anyway I32LLP64 have 4-byte longs, so they should work anyway with
>> these tests.
>>
>>> >  They'd probably break
>>> >  horribly because with 99% likelihood somewhere there is an assumption
>>> >  that sizeof (long) == sizeof (void*).
>>
>> In the atomic ops headers possibly, yes.
>
> You couldn't use atomic op headers to exchange pointers too.  Maybe not  
> used by liburcu, but still a strong limitation.

Well the current atomic op headers are per-architecture. This should be
taken into account for the generic version you are proposing I guess.

>
> Some time we should also add double-long compare-and-swap, that's very  
> useful for lock-free lists.

Yes, good idea! Although this won't be available on all architectures.
We might have to think of a mutex-based compatibility layer for these.

Do you have pointers to papers describing this double-wide CAS
linked-list structure ? I wonder if we could use a clever RCU structure
to mimick the double-wide CAS.

Thanks,

Mathieu

>
> Paolo
>
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-- 
Mathieu Desnoyers
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