Re: [PATCH v3 3/3] IB/core: Obtain subnet_prefix from cache in IB devices.

[Haakon Bugge]

> On 9 Jun 2021, at 12:40, Leon Romanovsky <leon@xxxxxxxxxx> wrote:
> 
> On Wed, Jun 09, 2021 at 09:26:03AM +0000, Anand Khoje wrote:
>> Hi Leon,
> 
> Please don't do top-posting.
> 
> 
>> 
>> The set_bit()/clear_bit() and enum ib_port_data_flags  has been added as a device that can be used for future enhancements. 
>> Also, usage of set_bit()/clear_bit() ensures the operations on this bit is atomic.
> 
> The bitfield variables are better suit this use case.
> Let's don't overcomplicate code without the reason.

The problem is always that people tend to build on what's in there. For example, look at the bitfields in rdma_id_private, tos_set,  timeout_set, and min_rnr_timer_set.

What do you think will happen when, let's say, rdma_set_service_type() and rdma_set_ack_timeout() are called in close proximity in time? There is no locking, and the RMW will fail intermittently.


Thxs, Håkon

> 
> Thanks
> 
>> 
>> Thanks,
>> Anand
>> 
>> -----Original Message-----
>> From: Leon Romanovsky <leon@xxxxxxxxxx> 
>> Sent: Wednesday, June 9, 2021 2:06 PM
>> To: Anand Khoje <anand.a.khoje@xxxxxxxxxx>
>> Cc: linux-rdma@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dledford@xxxxxxxxxx; jgg@xxxxxxxx; Haakon Bugge <haakon.bugge@xxxxxxxxxx>
>> Subject: Re: [PATCH v3 3/3] IB/core: Obtain subnet_prefix from cache in IB devices.
>> 
>> On Wed, Jun 09, 2021 at 11:25:34AM +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@xxxxxxxxxx>
>>> Signed-off-by: Haakon Bugge <haakon.bugge@xxxxxxxxxx>
>>> 
>>> ---
>>> 
>>> v1 -> v2:
>>>    -	Split the v1 patch in 3 patches as per Leon's suggestion.
>>> 
>>> v2 -> v3:
>>>    -	Added changes as per Mark Zhang's suggestion of clearing
>>>    	flags in git_table_cleanup_one().
>>> 
>>> ---
>>> 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(-)
>> 
>> Why did you use clear_bit/test_bit API? I would expect it for the bitmap, but for such simple thing, the simple "u8 is_cached_init : 1;"
>> will do the same trick.
>> 
>> Thanks
>> 
>>> 
>>> diff --git a/drivers/infiniband/core/cache.c 
>>> b/drivers/infiniband/core/cache.c index e957f0c915a3..94a8653a72c5 
>>> 100644
>>> --- a/drivers/infiniband/core/cache.c
>>> +++ b/drivers/infiniband/core/cache.c
>>> @@ -917,9 +917,12 @@ static void gid_table_cleanup_one(struct 
>>> ib_device *ib_dev)  {
>>> 	u32 p;
>>> 
>>> -	rdma_for_each_port (ib_dev, p)
>>> +	rdma_for_each_port (ib_dev, p) {
>>> +		clear_bit(IB_PORT_CACHE_INITIALIZED,
>>> +			&ib_dev->port_data[p].flags);
>>> 		cleanup_gid_table_port(ib_dev, p,
>>> 				       ib_dev->port_data[p].cache.gid);
>>> +	}
>>> }
>>> 
>>> static int gid_table_setup_one(struct ib_device *ib_dev) @@ -1623,6 
>>> +1626,8 @@ int ib_cache_setup_one(struct ib_device *device)
>>> 		err = ib_cache_update(device, p, true);
>>> 		if (err)
>>> 			return err;
>>> +		set_bit(IB_PORT_CACHE_INITIALIZED,
>>> +			&device->port_data[p].flags);
>>> 	}
>>> 
>>> 	return 0;
>>> diff --git a/drivers/infiniband/core/device.c 
>>> b/drivers/infiniband/core/device.c
>>> index 595128b26c34..e8e7b0a61411 100644
>>> --- a/drivers/infiniband/core/device.c
>>> +++ b/drivers/infiniband/core/device.c
>>> @@ -2059,6 +2059,15 @@ static int __ib_query_port(struct ib_device *device,
>>> 	    IB_LINK_LAYER_INFINIBAND)
>>> 		return 0;
>>> 
>>> +	if (!ib_cache_is_initialised(device, port_num))
>>> +		goto query_gid_from_device;
>>> +
>>> +	ib_get_cached_subnet_prefix(device, port_num,
>>> +				    &port_attr->subnet_prefix);
>>> +
>>> +	return 0;
>>> +
>>> +query_gid_from_device:
>>> 	err = device->ops.query_gid(device, port_num, 0, &gid);
>>> 	if (err)
>>> 		return err;
>>> diff --git a/include/rdma/ib_cache.h b/include/rdma/ib_cache.h index 
>>> 226ae3702d8a..1526fc6637eb 100644
>>> --- a/include/rdma/ib_cache.h
>>> +++ b/include/rdma/ib_cache.h
>>> @@ -114,4 +114,10 @@ ssize_t rdma_query_gid_table(struct ib_device *device,
>>> 			     struct ib_uverbs_gid_entry *entries,
>>> 			     size_t max_entries);
>>> 
>>> +static inline bool ib_cache_is_initialised(struct ib_device *device,
>>> +					  u8 port_num)
>>> +{
>>> +	return test_bit(IB_PORT_CACHE_INITIALIZED,
>>> +			&device->port_data[port_num].flags);
>>> +}
>>> #endif /* _IB_CACHE_H */
>>> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h index 
>>> 41cbec516424..ad2a55e3a2ee 100644
>>> --- a/include/rdma/ib_verbs.h
>>> +++ b/include/rdma/ib_verbs.h
>>> @@ -2169,6 +2169,10 @@ struct ib_port_immutable {
>>> 	u32                           max_mad_size;
>>> };
>>> 
>>> +enum ib_port_data_flags {
>>> +	IB_PORT_CACHE_INITIALIZED = 1 << 0,
>>> +};
>>> +
>>> struct ib_port_data {
>>> 	struct ib_device *ib_dev;
>>> 
>>> @@ -2178,6 +2182,8 @@ struct ib_port_data {
>>> 
>>> 	spinlock_t netdev_lock;
>>> 
>>> +	unsigned long flags;
>>> +
>>> 	struct list_head pkey_list;
>>> 
>>> 	struct ib_port_cache cache;
>>> --
>>> 2.27.0
>>>