Message-ID: <48c019b3-6748-4f89-9735-af66bbc7e65d@blackwall.org>
Date: Tue, 15 Apr 2025 17:15:22 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 edumazet@...gle.com, andrew+netdev@...n.ch, horms@...nel.org,
 petrm@...dia.com
Subject: Re: [PATCH net-next 00/15] vxlan: Convert FDB table to rhashtable

On 4/15/25 15:11, Ido Schimmel wrote:
> The VXLAN driver currently stores FDB entries in a hash table with a
> fixed number of buckets (256), resulting in reduced performance as the
> number of entries grows. This patchset solves the issue by converting
> the driver to use rhashtable which maintains a more or less constant
> performance regardless of the number of entries.
> 
> Measured transmitted packets per second using a single pktgen thread
> with varying number of entries when the transmitted packet always hits
> the default entry (worst case):
> 
> Number of entries | Improvement
> ------------------|------------
> 1k                | +1.12%
> 4k                | +9.22%
> 16k               | +55%
> 64k               | +585%
> 256k              | +2460%
> 
> The first patches are preparations for the conversion in the last patch.
> Specifically, the series is structured as follows:
> 
> Patch #1 adds RCU read-side critical sections in the Tx path when
> accessing FDB entries. Targeting at net-next as I am not aware of any
> issues due to this omission despite the code being structured that way
> for a long time. Without it, traces will be generated when converting
> FDB lookup to rhashtable_lookup().
> 
> Patch #2-#5 simplify the creation of the default FDB entry (all-zeroes).
> Current code assumes that insertion into the hash table cannot fail,
> which will no longer be true with rhashtable.
> 
> Patches #6-#10 add FDB entries to a linked list for entry traversal
> instead of traversing over them using the fixed size hash table which is
> removed in the last patch.
> 
> Patches #11-#12 add wrappers for FDB lookup that make it clear when each
> should be used along with lockdep annotations. Needed as a preparation
> for rhashtable_lookup() that must be called from an RCU read-side
> critical section.
> 
> Patch #13 treats dst cache initialization errors as non-fatal. See more
> info in the commit message. The current code happens to work because
> insertion into the fixed size hash table is slow enough for the per-CPU
> allocator to be able to create new chunks of per-CPU memory.
> 
> Patch #14 adds an FDB key structure that includes the MAC address and
> source VNI. To be used as rhashtable key.
> 
> Patch #15 does the conversion to rhashtable.
> 
> Ido Schimmel (15):
>   vxlan: Add RCU read-side critical sections in the Tx path
>   vxlan: Simplify creation of default FDB entry
>   vxlan: Insert FDB into hash table in vxlan_fdb_create()
>   vxlan: Unsplit default FDB entry creation and notification
>   vxlan: Relocate assignment of default remote device
>   vxlan: Use a single lock to protect the FDB table
>   vxlan: Add a linked list of FDB entries
>   vxlan: Use linked list to traverse FDB entries
>   vxlan: Convert FDB garbage collection to RCU
>   vxlan: Convert FDB flushing to RCU
>   vxlan: Rename FDB Tx lookup function
>   vxlan: Create wrappers for FDB lookup
>   vxlan: Do not treat dst cache initialization errors as fatal
>   vxlan: Introduce FDB key structure
>   vxlan: Convert FDB table to rhashtable
> 
>  drivers/net/vxlan/vxlan_core.c      | 542 ++++++++++++----------------
>  drivers/net/vxlan/vxlan_private.h   |  11 +-
>  drivers/net/vxlan/vxlan_vnifilter.c |   8 +-
>  include/net/vxlan.h                 |   5 +-
>  4 files changed, 248 insertions(+), 318 deletions(-)
> 

Nice work!
For the set:
Reviewed-by: Nikolay Aleksandrov <razor@...ckwall.org>

Cheers,
 Nik

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