linux-kernel - Re: [PATCH v4 for-next 3/3] IB/core: Obtain subnet

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Date:   Wed, 16 Jun 2021 13:13:51 +0530
From:   Anand Khoje <anand.a.khoje@...cle.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        dledford@...hat.com, jgg@...pe.ca, haakon.bugge@...cle.com
Subject: Re: [PATCH v4 for-next 3/3] IB/core: Obtain subnet_prefix from cache
 in IB devices

On 6/16/2021 1:00 PM, Leon Romanovsky wrote:
> On Wed, Jun 16, 2021 at 12:22:13PM +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.
>>
>> In the situation of an event causing cache update, the subnet_prefix
>> will get retrieved from newly updated GID cache in ib_cache_update(),
>> so that we do not end up reading a stale value from cache via
>> ib_query_port().
>>
>> Fixes: fad61ad ("IB/core: Add subnet prefix to port info")
>> Suggested-by: Leon Romanovsky <leonro@...dia.com>
>> Suggested-by: Aru Kolappan <aru.kolappan@...cle.com>
>> Signed-off-by: Anand Khoje <anand.a.khoje@...cle.com>
>> Signed-off-by: Haakon Bugge <haakon.bugge@...cle.com>
>> ---
> 
> <...>
> 
>> @@ -1523,13 +1526,21 @@ static int config_non_roce_gid_cache(struct ib_device *device,
>>   	device->port_data[port].cache.lmc = tprops->lmc;
>>   	device->port_data[port].cache.port_state = tprops->state;
>>   
>> -	device->port_data[port].cache.subnet_prefix = tprops->subnet_prefix;
>> +	ret = rdma_query_gid(device, port, 0, &gid);
>> +	if (ret) {
>> +		write_unlock_irq(&device->cache.lock);
> 
> And this patch can't compile. It should be cache_lock and not cache.lock.
> 
> Thanks
> 
Unfortunate typo from my end. Thanks for pointing this out. I will share 
the updated patch.