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From: Tiwei Bie <tiwei.bie@intel.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: dev@dpdk.org, yliu@fridaylinux.org, jfreiman@redhat.com,
	mst@redhat.com, vkaplans@redhat.com, jasowang@redhat.com,
	lei.a.yao@intel.com, cunming.liang@intel.com
Subject: Re: [dpdk-dev] [PATCH 03/21] vhost: protect virtio_net device struct
Date: Tue, 5 Sep 2017 18:07:51 +0800	[thread overview]
Message-ID: <20170905100751.GA7290@debian-ZGViaWFuCg> (raw)
In-Reply-To: <68468145-5b45-5875-b37f-35df3482379a@redhat.com>

On Tue, Sep 05, 2017 at 11:24:14AM +0200, Maxime Coquelin wrote:
> On 09/05/2017 06:45 AM, Tiwei Bie wrote:
> > On Thu, Aug 31, 2017 at 11:50:05AM +0200, Maxime Coquelin wrote:
> > > virtio_net device might be accessed while being reallocated
> > > in case of NUMA awareness. This case might be theoretical,
> > > but it will be needed anyway to protect vrings pages against
> > > invalidation.
> > > 
> > > The virtio_net devs are now protected with a readers/writers
> > > lock, so that before reallocating the device, it is ensured
> > > that it is not being referenced by the processing threads.
> > > 
> > [...]
> > > +struct virtio_net *
> > > +get_device(int vid)
> > > +{
> > > +	struct virtio_net *dev;
> > > +
> > > +	rte_rwlock_read_lock(&vhost_devices[vid].lock);
> > > +
> > > +	dev = __get_device(vid);
> > > +	if (unlikely(!dev))
> > > +		rte_rwlock_read_unlock(&vhost_devices[vid].lock);
> > > +
> > > +	return dev;
> > > +}
> > > +
> > > +void
> > > +put_device(int vid)
> > > +{
> > > +	rte_rwlock_read_unlock(&vhost_devices[vid].lock);
> > > +}
> > > +
> > 
> > This patch introduced a per-device rwlock which needs to be acquired
> > unconditionally in the data path. So for each vhost device, the IO
> > threads of different queues will need to acquire/release this lock
> > during each enqueue and dequeue operation, which will cause cache
> > contention when multiple queues are enabled and handled by different
> > cores. With this patch alone, I saw ~7% performance drop when enabling
> > 6 queues to do 64bytes iofwd loopback test. Is there any way to avoid
> > introducing this lock to the data path?
> 
> First, I'd like to thank you for running the MQ test.
> I agree it may have a performance impact in this case.
> 
> This lock has currently two purposes:
> 1. Prevent referencing freed virtio_dev struct in case of numa_realloc.
> 2. Protect vring pages against invalidation.
> 
> For 2., it can be fixed by using the per-vq IOTLB lock (it was not the
> case in my early prototypes that had per device IOTLB cache).
> 
> For 1., this is an existing problem, so we might consider it is
> acceptable to keep current state. Maybe it could be improved by only
> reallocating in case VQ0 is not on the right NUMA node, the other VQs
> not being initialized at this point.
> 
> If we do this we might be able to get rid of this lock, I need some more
> time though to ensure I'm not missing something.
> 
> What do you think?
> 

Cool. So it's possible that the lock in the data path will be
acquired only when the IOMMU feature is enabled. It will be
great!

Besides, I just did a very simple MQ test to verify my thoughts.
Lei (CC'ed in this mail) may do a thorough performance test for
this patch set to evaluate the performance impacts.

Best regards,
Tiwei Bie

  reply	other threads:[~2017-09-05 10:07 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-31  9:50 [dpdk-dev] [PATCH 00/21] Vhost-user: Implement device IOTLB support Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 01/21] Revert "vhost: workaround MQ fails to startup" Maxime Coquelin
2017-09-07 11:54   ` Yuanhan Liu
2017-09-07 12:59     ` Maxime Coquelin
2017-09-24 10:41       ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 02/21] vhost: make error handling consistent in rx path Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 03/21] vhost: protect virtio_net device struct Maxime Coquelin
2017-09-05  4:45   ` Tiwei Bie
2017-09-05  9:24     ` Maxime Coquelin
2017-09-05 10:07       ` Tiwei Bie [this message]
2017-09-05 11:00         ` Maxime Coquelin
2017-09-06  1:15           ` Tiwei Bie
2017-09-06  2:59             ` Stephen Hemminger
2017-09-06  7:50               ` Maxime Coquelin
2017-09-06  7:15             ` Maxime Coquelin
2017-09-06  7:30               ` Tiwei Bie
2017-09-06 20:02                 ` Maxime Coquelin
2017-09-07  5:08                   ` Tiwei Bie
2017-09-07 13:44   ` Yuanhan Liu
2017-09-07 14:01     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 04/21] vhost: prepare send_vhost_message() to slave requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 05/21] vhost: add support to slave requests channel Maxime Coquelin
2017-09-05  4:19   ` Tiwei Bie
2017-09-05  8:18     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 06/21] vhost: declare missing IOMMU-related definitions for old kernels Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 07/21] vhost: add iotlb helper functions Maxime Coquelin
2017-09-05  6:02   ` Tiwei Bie
2017-09-05 15:16     ` Maxime Coquelin
2017-09-08  8:08   ` Yuanhan Liu
2017-09-08  8:24     ` Maxime Coquelin
2017-09-08  8:36       ` Yuanhan Liu
2017-09-08  8:50         ` Maxime Coquelin
2017-09-08  9:21           ` Yuanhan Liu
2017-09-08  9:28             ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 08/21] vhost: iotlb: add pending miss request list and helpers Maxime Coquelin
2017-09-05  7:11   ` Tiwei Bie
2017-09-05 15:18     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 09/21] vhost-user: add support to IOTLB miss slave requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 10/21] vhost: initialize vrings IOTLB caches Maxime Coquelin
2017-09-04 13:57   ` Remy Horton
2017-09-04 15:45     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 11/21] vhost-user: handle IOTLB update and invalidate requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 12/21] vhost: introduce guest IOVA to backend VA helper Maxime Coquelin
2017-09-05  4:14   ` Tiwei Bie
2017-09-05  7:05     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 13/21] vhost: use the guest IOVA to host " Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 14/21] vhost: enable rings at the right time Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 15/21] vhost: don't dereference invalid dev pointer after its reallocation Maxime Coquelin
2017-09-04 13:58   ` Remy Horton
2017-08-31  9:50 ` [dpdk-dev] [PATCH 16/21] vhost: postpone rings addresses translation Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 17/21] vhost-user: translate ring addresses when IOMMU enabled Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 18/21] vhost-user: iommu: postpone device creation until ring are mapped Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 19/21] vhost: iommu: Invalidate vring in case of matching IOTLB invalidate Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 20/21] vhost: enable IOMMU support Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 21/21] vhost: iotlb: reduce iotlb read lock usage Maxime Coquelin
2017-09-11  4:18   ` Yuanhan Liu
2017-09-11  7:34     ` Maxime Coquelin
2017-09-11  9:39       ` Yuanhan Liu
2017-09-04 13:58 ` [dpdk-dev] [PATCH 00/21] Vhost-user: Implement device IOTLB support Remy Horton

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