From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=40494 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OOtlI-0004Qp-Fq for qemu-devel@nongnu.org; Wed, 16 Jun 2010 10:38:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OOtlH-0003QC-CB for qemu-devel@nongnu.org; Wed, 16 Jun 2010 10:38:40 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:49484) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OOtlH-0003Q4-9v for qemu-devel@nongnu.org; Wed, 16 Jun 2010 10:38:39 -0400 Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e6.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o5GEbA2P011070 for ; Wed, 16 Jun 2010 10:37:10 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o5GEcYrE1744938 for ; Wed, 16 Jun 2010 10:38:34 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o5GEcXhU002114 for ; Wed, 16 Jun 2010 10:38:34 -0400 Message-ID: <4C18E1E8.3030606@linux.vnet.ibm.com> Date: Wed, 16 Jun 2010 09:38:32 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets References: <20100616115404.10988.62371.stgit@localhost.localdomain> <20100616115656.10988.96529.stgit@localhost.localdomain> <4C18C4C8.8090901@redhat.com> <20100616142236.GA20052@shareable.org> <4C18DFD7.1090102@redhat.com> In-Reply-To: <4C18DFD7.1090102@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Gautham R Shenoy , Qemu-development List , "Aneesh Kumar K.V" , Corentin Chary , Avi Kivity On 06/16/2010 09:29 AM, Paolo Bonzini wrote: > On 06/16/2010 04:22 PM, Jamie Lokier wrote: >> Paolo Bonzini wrote: >>> These should be (at least for now) block-obj-$(CONFIG_POSIX). >>> >>>> + while (QTAILQ_EMPTY(&(queue->request_list))&& >>>> + (ret != ETIMEDOUT)) { >>>> + ret = qemu_cond_timedwait(&(queue->cond), >>>> + &(queue->lock), 10*100000); >>>> + } >>> >>> Using qemu_cond_timedwait is a hack for not properly broadcasting the >>> condvar in flush_threadlet_queue. >> >> Are you sure? It looks like it also expires idle threads after a >> fixed amount of idle time. > > Unnecessary idle threads are immediately expired as soon as the > threadlet exits if ncecessary, since here If a threadlet is waiting to consume more work, unless we do a pthread_cancel (I dislike cancellation) it will keep waiting until it gets more work (which would mean it's not actually idle)... > + queue->idle_threads++; > + > +check_exit: > + if (queue->exit || ((queue->idle_threads > 0) && > + (queue->cur_threads > queue->min_threads))) { > + /* We exit the queue or we retain minimum number of > threads */ > + break; > + } > > queue->idle_threads > 0 will always be true (so maybe that should be > changed into an assertion: "this thread is idle, so there must be idle > threads"). queue->exit could be true though so it's necessary to at least check that condition. I agree though that via the normal fall through path, queue->idle_threads can never be non-zero. Regards, Anthony Liguori > The min/max_threads parameters of the queue are currently immutable, > so it can never happen that a thread has to be expired while it's > waiting. It may well become true in the future, in which case the > condvar will have to be broadcast when min_threads changes. > > I may well be wrong of course. :) I think the code has been modified such that you are correct. > Paolo