From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH-RFC 2/2] eventfd: EFD_STATE flag Date: Tue, 04 Aug 2009 12:17:44 +0300 Message-ID: <4A77FCB8.1000205@redhat.com> References: <20090728175538.GC21549@redhat.com> <4A76FDB2.7080706@redhat.com> <20090803151426.GA3630@redhat.com> <4A770260.5000507@redhat.com> <20090803165708.GB3630@redhat.com> <4A77F6EF.8010002@redhat.com> <20090804085406.GA3311@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: davidel@xmailserver.org, gleb@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: "Michael S. Tsirkin" Return-path: Received: from mx2.redhat.com ([66.187.237.31]:41061 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932596AbZHDJMY (ORCPT ); Tue, 4 Aug 2009 05:12:24 -0400 In-Reply-To: <20090804085406.GA3311@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/04/2009 11:54 AM, Michael S. Tsirkin wrote: > On Tue, Aug 04, 2009 at 11:53:03AM +0300, Avi Kivity wrote: > >> On 08/03/2009 07:57 PM, Michael S. Tsirkin wrote: >> >>>> Why not do it at the point of the write? >>>> >>>> if (value != ctx->count) { >>>> ctx->count = value; >>>> wake_things_up(); >>>> } >>>> >>>> >>> What if write comes before read? >>> >>> >> The read will get the new value. >> > > Yes :) But how does read know it should not block? > If a different read comes after the write but after our read, it will have transferred the value, resulting in the same situation. I think reads should never block with a state based mechanism. -- error compiling committee.c: too many arguments to function