Revision 259039fa30457986929a324d769f543c1509987f authored by David S. Miller on 07 February 2020, 10:36:22 UTC, committed by David S. Miller on 07 February 2020, 10:36:22 UTC
Ong Boon Leong says:
====================
net: stmmac: general fixes for Ethernet functionality
1/5: It ensures that the previous value of GMAC_VLAN_TAG register is
read first before for updating the register.
2/5: Similar to 2/6 patch but it is a fix for XGMAC_VLAN_TAG register
as requested by Jose Abreu.
3/5: It ensures the GMAC IP v4.xx and above behaves correctly to:-
ip link set <devname> multicast off|on
4/5: Added similar IFF_MULTICAST flag for xgmac2, similar to 4/6.
5/5: It ensures PCI platform data is using plat->phy_interface.
Changes from v4:-
patch 1/6 - this patch is dropped now and will take the input on
handling return value from netif_set_real_num_rx|
tx_queues() in future patch series.
v3:-
patch 1/6 - add rtnl_lock() and rtnl_unlock() for stmmac_hw_setup()
called inside stmmac_resume()
patch 3/6 - Added new patch to fix XGMAC_VLAN_TAG register writting
v2:-
patch 1/5 - added control for rtnl_lock() & rtnl_unlock() to ensure
they are used forstmmac_resume()
patch 4/5 - added IFF_MULTICAST flag check for xgmac to ensure
multicast works correctly.
v1:-
- Drop v1 patches (1/7, 3/7 & 4/7) that are not valid.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
percpu-rw-semaphore.txt
====================
Percpu rw semaphores
====================
Percpu rw semaphores is a new read-write semaphore design that is
optimized for locking for reading.
The problem with traditional read-write semaphores is that when multiple
cores take the lock for reading, the cache line containing the semaphore
is bouncing between L1 caches of the cores, causing performance
degradation.
Locking for reading is very fast, it uses RCU and it avoids any atomic
instruction in the lock and unlock path. On the other hand, locking for
writing is very expensive, it calls synchronize_rcu() that can take
hundreds of milliseconds.
The lock is declared with "struct percpu_rw_semaphore" type.
The lock is initialized percpu_init_rwsem, it returns 0 on success and
-ENOMEM on allocation failure.
The lock must be freed with percpu_free_rwsem to avoid memory leak.
The lock is locked for read with percpu_down_read, percpu_up_read and
for write with percpu_down_write, percpu_up_write.
The idea of using RCU for optimized rw-lock was introduced by
Eric Dumazet <eric.dumazet@gmail.com>.
The code was written by Mikulas Patocka <mpatocka@redhat.com>
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