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,
lei.a.yao@intel.com, cunming.liang@intel.com
Subject: Re: [dpdk-dev] [PATCH 03/21] vhost: protect virtio_net device struct
Date: Wed, 6 Sep 2017 09:15:47 +0200 [thread overview]
Message-ID: <06b50f42-9151-9b94-646e-e2e2b153a957@redhat.com> (raw)
In-Reply-To: <20170906011459.GA3965@debian-ZGViaWFuCg>
Hi Tiwei,
On 09/06/2017 03:15 AM, Tiwei Bie wrote:
> On Tue, Sep 05, 2017 at 01:00:42PM +0200, Maxime Coquelin wrote:
>> On 09/05/2017 12:07 PM, Tiwei Bie wrote:
>>> 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.
>>
>> I'll try to post v2 this week including the proposed change.
>> Maybe it'll be better Lei waits for the v2.
>>
>
> Cool. Sure. Thank you! :)
I have done the changes, you can find the v2 on my gitlab repo:
https://gitlab.com/mcoquelin/dpdk-next-virtio/commits/vhost_iotlb_v2
I'm testing it right now, but if you'd like to run some early benchmark
before I post the series, there it is!
Thanks,
Maxime
> Best regards,
> Tiwei Bie
>
next prev parent reply other threads:[~2017-09-06 7:15 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=06b50f42-9151-9b94-646e-e2e2b153a957@redhat.com \
--to=maxime.coquelin@redhat.com \
--cc=cunming.liang@intel.com \
--cc=dev@dpdk.org \
--cc=jasowang@redhat.com \
--cc=jfreiman@redhat.com \
--cc=lei.a.yao@intel.com \
--cc=mst@redhat.com \
--cc=tiwei.bie@intel.com \
--cc=vkaplans@redhat.com \
--cc=yliu@fridaylinux.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).