Merge branch 'net_proc_perf'
Jia He says:
====================
Reduce cache miss for snmp_fold_field
In a PowerPc server with large cpu number(160), besides commit
a3a773726c9f ("net: Optimize snmp stat aggregation by walking all
the percpu data at once"), I watched several other snmp_fold_field
callsites which would cause high cache miss rate.
test source code:
================
My simple test case, which read from the procfs items endlessly:
/***********************************************************/
int main(int argc, char **argv)
{
int i;
int fd = -1 ;
int rdsize = 0;
char buf[LINELEN+1];
buf[LINELEN] = 0;
memset(buf,0,LINELEN);
if(1 >= argc) {
printf("file name empty\n");
return -1;
}
fd = open(argv[1], O_RDWR, 0644);
if(0 > fd){
printf("open error\n");
return -2;
}
for(i=0;i<0xffffffff;i++) {
while(0 < (rdsize = read(fd,buf,LINELEN))){
//nothing here
}
lseek(fd, 0, SEEK_SET);
}
close(fd);
return 0;
}
/**********************************************************/
compile and run:
================
gcc test.c -o test
perf stat -d -e cache-misses ./test /proc/net/snmp
perf stat -d -e cache-misses ./test /proc/net/snmp6
perf stat -d -e cache-misses ./test /proc/net/sctp/snmp
perf stat -d -e cache-misses ./test /proc/net/xfrm_stat
before the patch set:
====================
Performance counter stats for 'system wide':
355911097 cache-misses [40.08%]
2356829300 L1-dcache-loads [60.04%]
355642645 L1-dcache-load-misses # 15.09% of all L1-dcache hits [60.02%]
346544541 LLC-loads [59.97%]
389763 LLC-load-misses # 0.11% of all LL-cache hits [40.02%]
6.245162638 seconds time elapsed
After the patch set:
===================
Performance counter stats for 'system wide':
194992476 cache-misses [40.03%]
6718051877 L1-dcache-loads [60.07%]
194871921 L1-dcache-load-misses # 2.90% of all L1-dcache hits [60.11%]
187632232 LLC-loads [60.04%]
464466 LLC-load-misses # 0.25% of all LL-cache hits [39.89%]
6.868422769 seconds time elapsed
The cache-miss rate can be reduced from 15% to 2.9%
changelog
=========
v6:
- correct v5
v5:
- order local variables from longest to shortest line
v4:
- move memset into one block of if statement in snmp6_seq_show_item
- remove the changes in netstat_seq_show considerred the stack usage is too large
v3:
- introduce generic interface (suggested by Marcelo Ricardo Leitner)
- use max_t instead of self defined macro (suggested by David Miller)
v2:
- fix bug in udplite statistics.
- snmp_seq_show is split into 2 parts
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
