forked from Minki/linux
2f970d8357
Using __get_cpu_var(obj) is slightly faster than per_cpu_ptr(obj, raw_smp_processor_id()). 1) Smaller code and memory use For static and small objects, DEFINE_PER_CPU(type, object) is preferred over a alloc_percpu() : Better and smaller code to access them, and no extra memory (storing the pointer, and the percpu array of pointers) x86_64 code before patch mov 1237577(%rip),%rax # ffffffff803e5990 <rt_cache_stat> not %rax # part of per_cpu machinery mov %gs:0x3c,%edx # get cpu number movslq %edx,%rdx # extend 32 bits cpu number to 64 bits mov (%rax,%rdx,8),%rax # get the pointer for this cpu incl 0x38(%rax) x86_64 code after patch mov $per_cpu__rt_cache_stat,%rdx mov %gs:0x48,%rax # get percpu data offset incl 0x38(%rax,%rdx,1) 2) False sharing avoidance for SMP : For a small NR_CPUS, the array of per cpu pointers allocated in alloc_percpu() can be <= 32 bytes. This let slab code gives a part of a cache line. If the other part of this 64 bytes (or 128 bytes) cache line is used by a mostly written object, we can have false sharing and expensive per_cpu_ptr() operations. Size of rt_cache_stat is 64 bytes, so this patch is not a danger of a too big increase of bss (in UP mode) or static per_cpu data for SMP (PERCPU_ENOUGH_ROOM is currently 32768 bytes) Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| 802 | ||
| 8021q | ||
| appletalk | ||
| atm | ||
| ax25 | ||
| bluetooth | ||
| bridge | ||
| core | ||
| dccp | ||
| decnet | ||
| econet | ||
| ethernet | ||
| ieee80211 | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| key | ||
| lapb | ||
| llc | ||
| netfilter | ||
| netlink | ||
| netrom | ||
| packet | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| sunrpc | ||
| tipc | ||
| unix | ||
| wanrouter | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| nonet.c | ||
| socket.c | ||
| sysctl_net.c | ||
| TUNABLE | ||