Revision 89eb4d8d25722a0a0194cf7fa47ba602e32a6da7 authored by Vitaly Kuznetsov on 19 August 2019, 14:44:09 UTC, committed by Sasha Levin on 20 August 2019, 15:29:53 UTC
When building hv_kvp_daemon GCC-8.3 complains: hv_kvp_daemon.c: In function ‘kvp_get_ip_info.constprop’: hv_kvp_daemon.c:812:30: warning: ‘ip_buffer’ may be used uninitialized in this function [-Wmaybe-uninitialized] struct hv_kvp_ipaddr_value *ip_buffer; this seems to be a false positive: we only use ip_buffer when op == KVP_OP_GET_IP_INFO and it is only unset when op == KVP_OP_ENUMERATE. Silence the warning by initializing ip_buffer to NULL. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
1 parent d09bc83
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>
Computing file changes ...
