From cdd7abfdba9287a289c404dfdcb02316f9ffee7d Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 26 Jan 2017 17:01:19 +0000 Subject: [PATCH] iothread: enable AioContext polling by default 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 Message-id: 20170126170119.27876-1-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- iothread.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/iothread.c b/iothread.c index 7bedde87e9..257b01d5f1 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},