From mboxrd@z Thu Jan  1 00:00:00 1970
From: compudj@krystal.dyndns.org (Mathieu Desnoyers)
Date: Fri, 12 Nov 2010 07:29:39 -0500
Subject: [ltt-dev] [PATCH 2/2] introduce uatomic_and and uatomic_or
In-Reply-To: <4CDD31E7.1050500@redhat.com>
References: <1289552247-18130-1-git-send-email-pbonzini@redhat.com>
	<1289552247-18130-3-git-send-email-pbonzini@redhat.com>
	<20101112120846.GB27929@Krystal> <4CDD2F69.7020407@redhat.com>
	<20101112121900.GA29642@Krystal> <4CDD31E7.1050500@redhat.com>
Message-ID: <20101112122939.GA30826@Krystal>

* Paolo Bonzini (pbonzini at redhat.com) wrote:
> On 11/12/2010 01:19 PM, Mathieu Desnoyers wrote:
>> * Paolo Bonzini (pbonzini at redhat.com) wrote:
>>> Return nothing can be useful because it can be optimized on x86 as "lock
>>> orl (mem), reg/imm".  However, there are no other return-nothing atomic
>>> ops in uatomic_*.h so I decided not to provide this.
>>>
>>
>> How about we start by implementing uatomic_and/uatomic_or that return
>> void, and if we ever need uatomic_return_and/uatomic_return_or (see my
>> other mail), we add them ?
>
> I am using uatomic_or's return value in my call_rcu-with-futex, but I  
> don't need atomic-or-and-exchange really, I can even change it to a load  
> followed by an atomic or (it introduces a race but it is benign).

If the race does not matter, why do we need the new atomic op in the
first place ? ;)

>  Or I  
> can certainly use cmpxchg too.  Updated patches will come.
>
> Should I rename uatomic_add to uatomic_xchg_add too (I prefer this name  
> to uatomic_return_add)?

Renaming uatomic_add ? I don't understand what you are trying to achieve
here. uatomic_add returns void, doesn't it ?

(generally speaking, I agree that uatomic_xchg_op is nicer than
uatomic_return_op)

Thanks,

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com