linux-kernel - Re: [PATCH v2 3/3] IB/core: Obtain subnet

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Message-ID: <YLib5BhTX6tEMTfe@unreal>
Date:   Thu, 3 Jun 2021 12:07:48 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Anand Khoje <anand.a.khoje@...cle.com>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        dledford@...hat.com, jgg@...pe.ca, haakon.bugge@...cle.com
Subject: Re: [PATCH v2 3/3] IB/core: Obtain subnet_prefix from cache in IB
 devices

On Thu, Jun 03, 2021 at 12:20:24PM +0530, Anand Khoje wrote:
> ib_query_port() calls device->ops.query_port() to get the port
> attributes. The method of querying is device driver specific.
> The same function calls device->ops.query_gid() to get the GID and
> extract the subnet_prefix (gid_prefix).
> 
> The GID and subnet_prefix are stored in a cache. But they do not get
> read from the cache if the device is an Infiniband device. The
> following change takes advantage of the cached subnet_prefix.
> Testing with RDBMS has shown a significant improvement in performance
> with this change.
> 
> The function ib_cache_is_initialised() is introduced because
> ib_query_port() gets called early in the stage when the cache is not
> built while reading port immutable property.
> 
> In that case, the default GID still gets read from HCA for IB link-
> layer devices.
> 
> Fixes: fad61ad ("IB/core: Add subnet prefix to port info")
> Signed-off-by: Anand Khoje <anand.a.khoje@...cle.com>
> Signed-off-by: Haakon Bugge <haakon.bugge@...cle.com>
> ---
>  drivers/infiniband/core/cache.c  | 7 ++++++-
>  drivers/infiniband/core/device.c | 9 +++++++++
>  include/rdma/ib_cache.h          | 6 ++++++
>  include/rdma/ib_verbs.h          | 6 ++++++
>  4 files changed, 27 insertions(+), 1 deletion(-)

Can you please help me to understand how cache is updated?

There are a lot of calls to ib_query_port() and I wonder how callers can
get new GID after it was changed in already initialized cache.

Thanks