From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Tiwei Bie <tiwei.bie@intel.com>
Cc: dev@dpdk.org, yliu@fridaylinux.org, jfreiman@redhat.com,
mst@redhat.com, vkaplans@redhat.com, jasowang@redhat.com
Subject: Re: [dpdk-dev] [PATCH 03/21] vhost: protect virtio_net device struct
Date: Tue, 5 Sep 2017 11:24:14 +0200 [thread overview]
Message-ID: <68468145-5b45-5875-b37f-35df3482379a@redhat.com> (raw)
In-Reply-To: <20170905044516.GC31895@debian-ZGViaWFuCg>
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?
Thanks,
Maxime
> Best regards,
> Tiwei Bie
>
next prev parent reply other threads:[~2017-09-05 9:24 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 [this message]
2017-09-05 10:07 ` Tiwei Bie
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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