linux-kernel - Re: [PATCH vhost 0/7] vdpa/mlx5: Parallelize device suspend/resume

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Message-ID: <6582792d-8db2-4bc0-bf3a-248fe5c8fc56@nvidia.com>
Date: Wed, 7 Aug 2024 16:54:17 +0200
From: Dragos Tatulea <dtatulea@...dia.com>
To: Eugenio Perez Martin <eperezma@...hat.com>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Si-Wei Liu <si-wei.liu@...cle.com>, netdev@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
 virtualization@...ts.linux.dev
Subject: Re: [PATCH vhost 0/7] vdpa/mlx5: Parallelize device suspend/resume



On 07.08.24 15:25, Eugenio Perez Martin wrote:
> On Fri, Aug 2, 2024 at 9:24 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
>>
>> This series parallelizes the mlx5_vdpa device suspend and resume
>> operations through the firmware async API. The purpose is to reduce live
>> migration downtime.
>>
>> The series starts with changing the VQ suspend and resume commands
>> to the async API. After that, the switch is made to issue multiple
>> commands of the same type in parallel.
>>
> 
> There is a missed opportunity processing the CVQ MQ command here,
> isn't it? It can be applied on top in another series for sure.
> 
Initially I considered that it would complicate the code too much in
change_num_qps(). But in the current state of the patches it's doable.

Will send a V2 with an extra patch for this.

>> Finally, a bonus improvement is thrown in: keep the notifierd enabled
>> during suspend but make it a NOP. Upon resume make sure that the link
>> state is forwarded. This shaves around 30ms per device constant time.
>>
>> For 1 vDPA device x 32 VQs (16 VQPs), on a large VM (256 GB RAM, 32 CPUs
>> x 2 threads per core), the improvements are:
>>
>> +-------------------+--------+--------+-----------+
>> | operation         | Before | After  | Reduction |
>> |-------------------+--------+--------+-----------|
>> | mlx5_vdpa_suspend | 37 ms  | 2.5 ms |     14x   |
>> | mlx5_vdpa_resume  | 16 ms  | 5 ms   |      3x   |
>> +-------------------+--------+--------+-----------+
>>
> 
> Looks great :).
> 
> Apart from the nitpick,
>
> Acked-by: Eugenio Pérez <eperezma@...hat.com>
> 
> For the vhost part.
Thanks!

> 
> Thanks!
> 
>> Note for the maintainers:
>> The first patch contains changes for mlx5_core. This must be applied
>> into the mlx5-vhost tree [0] first. Once this patch is applied on
>> mlx5-vhost, the change has to be pulled from mlx5-vdpa into the vhost
>> tree and only then the remaining patches can be applied.
>>
>> [0] https://git.kernel.org/pub/scm/linux/kernel/git/mellanox/linux.git/log/?h=mlx5-vhost
>>
>> Dragos Tatulea (7):
>>   net/mlx5: Support throttled commands from async API
>>   vdpa/mlx5: Introduce error logging function
>>   vdpa/mlx5: Use async API for vq query command
>>   vdpa/mlx5: Use async API for vq modify commands
>>   vdpa/mlx5: Parallelize device suspend
>>   vdpa/mlx5: Parallelize device resume
>>   vdpa/mlx5: Keep notifiers during suspend but ignore
>>
>>  drivers/net/ethernet/mellanox/mlx5/core/cmd.c |  21 +-
>>  drivers/vdpa/mlx5/core/mlx5_vdpa.h            |   7 +
>>  drivers/vdpa/mlx5/net/mlx5_vnet.c             | 435 +++++++++++++-----
>>  3 files changed, 333 insertions(+), 130 deletions(-)
>>
>> --
>> 2.45.2
>>
>