From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39402) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cX93T-0003W3-WE for qemu-devel@nongnu.org; Fri, 27 Jan 2017 11:07:16 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cX93Q-0000bM-09 for qemu-devel@nongnu.org; Fri, 27 Jan 2017 11:07:15 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37924) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cX93P-0000bC-Pj for qemu-devel@nongnu.org; Fri, 27 Jan 2017 11:07:11 -0500 References: <20170126170119.27876-1-stefanha@redhat.com> From: Paolo Bonzini Message-ID: <5f274867-7189-5bcd-d64b-f5ff31b0d54c@redhat.com> Date: Fri, 27 Jan 2017 17:07:08 +0100 MIME-Version: 1.0 In-Reply-To: <20170126170119.27876-1-stefanha@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] iothread: enable AioContext polling by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi , qemu-devel@nongnu.org Cc: Christian Borntraeger , Karl Rister On 26/01/2017 18:01, Stefan Hajnoczi wrote: > IOThread AioContexts are likely to consist only of event sources like > virtqueue ioeventfds and LinuxAIO completion eventfds that are pollable > from userspace (without system calls). > > We recently merged the AioContext polling feature but didn't enable it > by default yet. I have gone back over the performance data on the > mailing list and picked a default polling value that gave good results. > > Let's enable AioContext polling by default so users don't have another > switch they need to set manually. If performance regressions are found > we can still disable this for the QEMU 2.9 release. > > Cc: Paolo Bonzini > Cc: Christian Borntraeger > Cc: Karl Rister > Signed-off-by: Stefan Hajnoczi > --- > iothread.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/iothread.c b/iothread.c > index 7bedde8..257b01d 100644 > --- a/iothread.c > +++ b/iothread.c > @@ -30,6 +30,12 @@ typedef ObjectClass IOThreadClass; > #define IOTHREAD_CLASS(klass) \ > OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD) > > +/* Benchmark results from 2016 on NVMe SSD drives show max polling times around > + * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32 > + * workloads. > + */ > +#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL > + > static __thread IOThread *my_iothread; > > AioContext *qemu_get_current_aio_context(void) > @@ -71,6 +77,13 @@ static int iothread_stop(Object *object, void *opaque) > return 0; > } > > +static void iothread_instance_init(Object *obj) > +{ > + IOThread *iothread = IOTHREAD(obj); > + > + iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT; > +} > + > static void iothread_instance_finalize(Object *obj) > { > IOThread *iothread = IOTHREAD(obj); > @@ -215,6 +228,7 @@ static const TypeInfo iothread_info = { > .parent = TYPE_OBJECT, > .class_init = iothread_class_init, > .instance_size = sizeof(IOThread), > + .instance_init = iothread_instance_init, > .instance_finalize = iothread_instance_finalize, > .interfaces = (InterfaceInfo[]) { > {TYPE_USER_CREATABLE}, > ACK Paolo