Re: [patch, v2.6.22-rc6] sys_time() speedup
From: Andrea Arcangeli
Date: Tue Jun 26 2007 - 20:16:27 EST
On Tue, Jun 26, 2007 at 10:13:31AM -0700, Ray Lee wrote:
> faster? Weird. It shouldn't. They must be doing something wrong,
> therefore the patch is stupid."
Just in case it's not obvious the above are Ray Lee words, mine not.
-----------
#!/usr/bin/env stap
# edited top.stp from systemtap
global syscalls
function print_top () {
printf ("SYSCALL\t\t\t\tCOUNT\n")
foreach ([name] in syscalls- limit 20)
printf("%-20s\t\t%5d\n",name, syscalls[name])
printf("--------------------------------------\n")
}
probe syscall.time {
syscalls[probefunc()]++
}
probe syscall.gettimeofday {
syscalls[probefunc()]++
}
# print top syscalls every 5 seconds
probe timer.ms(5000) {
print_top ()
}
-----------
The above while running various huge sql operations with real life
postgresql app running sql in loop for a minute or so (sorry no mysql
setup but the world isn't mysql, I'd rather want to see oracle if
something):
SYSCALL COUNT
sys_gettimeofday 4998
sys_time 120
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 9989
sys_time 185
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 15219
sys_time 335
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 21215
sys_time 428
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 26194
sys_time 629
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 30752
sys_time 734
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 37379
sys_time 976
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 42381
sys_time 1125
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 47722
sys_time 1391
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 53138
sys_time 1520
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 57499
sys_time 1651
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 62314
sys_time 1712
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 66874
sys_time 1827
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 71757
sys_time 2007
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 76335
sys_time 2240
SYSCALL COUNT
sys_gettimeofday 80469
sys_time 2354
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 85420
sys_time 2519
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 90662
sys_time 2648
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 95513
sys_time 2909
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 100767
sys_time 3111
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 106553
sys_time 3427
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 112300
sys_time 3673
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 115706
sys_time 3793
SYSCALL COUNT
sys_gettimeofday 119842
sys_time 3893
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 123054
sys_time 4113
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 126286
sys_time 4250
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 129077
sys_time 4396
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 132002
sys_time 4506
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 138518
sys_time 4800
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 143572
sys_time 4901
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 148621
sys_time 5069
Now if I play some music with projectm in the background:
SYSCALL COUNT
sys_gettimeofday 6337
sys_time 128
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 11462
sys_time 249
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 21905
sys_time 332
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 36205
sys_time 494
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 53792
sys_time 569
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 69699
sys_time 709
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 85663
sys_time 791
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 101427
sys_time 908
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 117199
sys_time 985
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 132963
sys_time 1100
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 148974
sys_time 1162
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 164677
sys_time 1288
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 180697
sys_time 1356
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 196517
sys_time 1479
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 209618
sys_time 1546
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 214914
sys_time 1726
--------------------------------------
SYSCALL COUNT
sys_gettimeofday 221257
sys_time 1798
If I listen some music on youtube.com:
SYSCALL COUNT
sys_gettimeofday 5151
sys32_gettimeofday 3951
sys_time 202
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 16427
sys_gettimeofday 10247
sys_time 306
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 42436
sys_gettimeofday 15633
sys_time 438
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 64931
sys_gettimeofday 21121
sys_time 509
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 94366
sys_gettimeofday 26399
sys_time 638
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 117573
sys_gettimeofday 33100
sys_time 722
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 137415
sys_gettimeofday 38357
sys_time 863
compat_sys_time 1
--------------------------------------
SYSCALL COUNT
sys32_gettimeofday 154831
sys_gettimeofday 43459
sys_time 933
compat_sys_time 1
Those aren't gettimeofday heavy users at all, they're the normal
"light" kernel users of the most common workloads. The sql wasn't
gettimeofday intensive either. The very heavy users will run hundred
thousands gettimeofday or more per second so they're not even
interesting to measure because the sys_time system time will be close
to zero compared to the gettimeofday one.
BTW, to run the above I had to disable vsyscall64 sysctl, my x2 would
never waste any time running sys_time or sys_gettimeofday in the first
place ;).
This patch may be a good tradeoff anyway, but IMHO it's not possible
to judje the idea of adding a branch to sys_gettimeofday to make
sys_time faster without knowing why mysql calls time() so
frequently. Even if you care only about the present and you don't care
about the future, mysql isn't the only db in the marketplace and like
I wrote in the other email the others I've seen were running floods of
gettimeofday (I repeat, some even went as far as giving an option to
call rdtsc directly on the few servers with tsc synchronized in smp).
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