From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1L6uor-0007t2-D2 for qemu-devel@nongnu.org; Sun, 30 Nov 2008 17:31:13 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1L6uop-0007pe-Av for qemu-devel@nongnu.org; Sun, 30 Nov 2008 17:31:12 -0500 Received: from [199.232.76.173] (port=57646 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1L6uop-0007pV-3j for qemu-devel@nongnu.org; Sun, 30 Nov 2008 17:31:11 -0500 Received: from yw-out-1718.google.com ([74.125.46.153]:19974) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1L6uoo-0002eK-QS for qemu-devel@nongnu.org; Sun, 30 Nov 2008 17:31:10 -0500 Received: by yw-out-1718.google.com with SMTP id 6so799970ywa.82 for ; Sun, 30 Nov 2008 14:31:09 -0800 (PST) Message-ID: <49331429.1090300@codemonkey.ws> Date: Sun, 30 Nov 2008 16:31:05 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [RFC 1/2] pci-dma-api-v1 References: <20081127123538.GC10348@random.random> <20081128015602.GA31011@random.random> <20081128185001.GD31011@random.random> <20081128191819.GA18031@shareable.org> In-Reply-To: <20081128191819.GA18031@shareable.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Andrea Arcangeli Jamie Lokier wrote: > Blue Swirl wrote: > >>> I wonder how can possibly aio_readv/writev be missing in posix aio? >>> Unbelievable. It'd be totally trivial to add those to glibc, much >>> easier infact than to pthread_create by hand, but how can we add a >>> dependency on a certain glibc version? Ironically it'll be more >>> user-friendly to add dependency on linux kernel-aio implementation >>> that is already available for ages and it's guaranteed to run faster >>> (or at least not slower). >>> >> There's also lio_listio that provides for vectored AIO. >> > > I think lio_listio is the missing aio_readv/writev. > > It's more versatile, and that'll by why POSIX never bothered with > aio_readv/writev. > No. lio_listio is a batch submission mechanism, not an operation. Each request maintains the same behavior as if they were submitted independently. This means if you're doing a write operation and you submit a vectored request via lio_listio, each portion of the vector has to complete before the other one. But most importantly, pthreads doesn't use readv/writev to implement lio_listio as has been mentioned elsewhere. Regards, Anthony Liguori > Doesn't explain why they didn't _start_ with aio_readv before > inventing lio_listio, but there you go. Unix history. > > -- Jamie > > >