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Date:   Wed, 16 Jun 2021 11:41:29 +0300
From:   Leon Romanovsky <leon@kernel.org>
To:     Anand Khoje <anand.a.khoje@oracle.com>
Cc:     linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
        dledford@redhat.com, jgg@ziepe.ca, haakon.bugge@oracle.com
Subject: Re: [PATCH v4 for-next 3/3] IB/core: Obtain subnet_prefix from cache
 in IB devices
Message-ID: <YMm5OWnN0242e970@unreal>
References: <20210616065213.987-1-anand.a.khoje@oracle.com>
 <20210616065213.987-4-anand.a.khoje@oracle.com>
 <YMmnyE+rpLIf6e0B@unreal>
 <ac8da9cf-9dec-a207-c80e-e9ee650b40fc@oracle.com>
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On Wed, Jun 16, 2021 at 01:12:51PM +0530, Anand Khoje wrote:
> On 6/16/2021 12:57 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@nvidia.com>
> > > Suggested-by: Aru Kolappan <aru.kolappan@oracle.com>
> > > Signed-off-by: Anand Khoje <anand.a.khoje@oracle.com>
> > > Signed-off-by: Haakon Bugge <haakon.bugge@oracle.com>
> > > ---
> > > 
> > > 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().
> > > v3 -> v4:
> > >      -   Removed the enum ib_port_data_flags and 8 byte flags from
> > >          struct ib_port_data, and the set_bit()/clear_bit() API
> > >          used to update this flag as that was not necessary.
> > >          Done to keep the code simple.
> > >      -   Added code to read subnet_prefix from updated GID cache in the
> > >          event of cache update. Prior to this change, ib_cache_update
> > >          was reading the value for subnet_prefix via ib_query_port(),
> > >          due to this patch, we ended up reading a stale cached value of
> > >          subnet_prefix.
> > > 
> > > ---
> > >   drivers/infiniband/core/cache.c  | 18 +++++++++++++++---
> > >   drivers/infiniband/core/device.c |  9 +++++++++
> > >   include/rdma/ib_cache.h          |  5 +++++
> > >   include/rdma/ib_verbs.h          |  1 +
> > >   4 files changed, 30 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/infiniband/core/cache.c b/drivers/infiniband/core/cache.c
> > > index 2325171..cd99c46 100644
> > > --- a/drivers/infiniband/core/cache.c
> > > +++ b/drivers/infiniband/core/cache.c
> > > @@ -917,9 +917,11 @@ 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) {
> > > +		ib_dev->port_data[p].cache_is_initialized = 0;
> > 
> > I think that this line is not needed, we are removing device anyway and
> > and query_port is not allowed at this stage.
> > 
> We have kept this for code completeness purposes. Just as we did with
> set_bit() and clear_bit() APIs.

You are not using *_bit() API now, so let's not clear here.
It is not completeness, but misleading. It gives false assumption
that cache_is_initialized is used later in the code.

> 
> > >   		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)
> > > @@ -1466,6 +1468,7 @@ static int config_non_roce_gid_cache(struct ib_device *device,
> > >   	struct ib_port_attr       *tprops = NULL;
> > >   	struct ib_pkey_cache      *pkey_cache = NULL;
> > >   	struct ib_pkey_cache      *old_pkey_cache = NULL;
> > > +	union ib_gid               gid;
> > >   	int                        i;
> > >   	int                        ret;
> > > @@ -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);
> > > +		goto err;
> > > +	}
> > > +
> > > +	device->port_data[port].cache.subnet_prefix =
> > > +			be64_to_cpu(gid.global.subnet_prefix);
> > > +
> > >   	write_unlock_irq(&device->cache_lock);
> > >   	if (enforce_security)
> > >   		ib_security_cache_change(device,
> > >   					 port,
> > > -					 tprops->subnet_prefix);
> > > +					 be64_to_cpu(gid.global.subnet_prefix));
> > >   	kfree(old_pkey_cache);
> > >   	kfree(tprops);
> > > @@ -1629,6 +1640,7 @@ int ib_cache_setup_one(struct ib_device *device)
> > >   		err = ib_cache_update(device, p, true, true, true);
> > >   		if (err)
> > >   			return err;
> > > +		device->port_data[p].cache_is_initialized = 1;
> > >   	}
> > >   	return 0;
> > > diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> > > index 7a617e4..57b9039 100644
> > > --- a/drivers/infiniband/core/device.c
> > > +++ b/drivers/infiniband/core/device.c
> > > @@ -2057,6 +2057,15 @@ 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;
> > 
> > IMHO, we don't need this new function and can access ib_port_data
> > directly. In device.c, we have plenty of places that does it.
> > 
> > Not critical.
> > 
> Added this function to have a way to check validity of cache, such that it
> could be used in future for the same check in areas to which ib_port_data is
> opaque.


It is ok, just call directly if (!device->port_data[port_num].cache_is_initialized).

Thanks