Re: IB/cma: Make timeout dependent on the subnet timeout

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

On 04/23/14 14:30, Hal Rosenstock wrote:
> On 4/22/2014 2:41 PM, Hefty, Sean wrote:
>>> +static u8 cma_get_ib_subnet_timeout(struct rdma_cm_id *id)
>>> +{
>>> +	struct ib_port_attr attr;
>>> +	int ret;
>>> +
>>> +	ret = ib_query_port(id->device, id->port_num, &attr);
>>> +	return ret == 0 ? attr.subnet_timeout : 18;
>>> +}
>>
>> Can we query the port once (or only on a change) and cache the result, rather than querying it for every request?
> 
> To be IBA spec compliant, SubnetTimeout could change so some new local
> event would need to be added and handled to avoid the requerying.
> 
> In practice, however, that's not very likely AFAIK.

Thanks Sean and Hal for the feedback.

Regarding SubnetTimeout changes: the code in
drivers/infiniband/core/cache.c already queues a work request after each
port state change. Inside that work request e.g. the P_Key cache is
updated. Would it be acceptable to modify ib_cache_update() such that it
also queries the port attributes and caches these ? Cached port
attributes could e.g. be stored in struct ib_port. However, doing so
would probably require to protect the port_list member in struct
ib_device against concurrent modifications of that list by the sysfs code.

Bart.

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