semaphore access speed


 
Thread Tools Search this Thread
Top Forums Programming semaphore access speed
# 22  
Old 09-23-2008
Otheus -
utimes is the call made by
Code:
 time <command>

It gives cumulative times for user and kernel, as well as cum process wall time.
Call it for a starting set of values and an ending set of values, then substract for a delta value.
# 23  
Old 09-23-2008
Sorry - a little off track - I don't see where the OP has tried running ltrace with syscalls enabled - or strace.

The differences probably are due to OS implementation - maybe a lot of calls to brk in one OS and not the other. It's worth the 2 minutes it takes to execute Otheus' code under strace on each box. That would rule out an odd kernel setting or some implementation "feature" as the root cause of the differences. If you see odd behavior, like a lot of system calls on one box and not on the the other, maybe someone can relate that to something useful.
# 24  
Old 09-23-2008
Quote:
Originally Posted by jim mcnamara
Otheus -
utimes is the call made by
Code:
 time <command>

It gives cumulative times for user and kernel, as well as cum process wall time.
Call it for a starting set of values and an ending set of values, then substract for a delta value.
I think you are confused. utime() and utimes() operate on an inode to change timestamps of files.
# 25  
Old 09-23-2008
to Otheus:
gprof -l complains about missing call-graph data, which I don't quite understand, but that is beyond the point in this thread.

to Jim:

On SCO
$ truss ./tstloop
semsys(1, 2819742, 2, 0, 0, 0) = 18827
semsys(0, 18827, 2, 6, 2147483024, 0) = 0
.
.
.
repeats on and on for 5,000,000 times, as coded.
I don't see any brk here.

On Linux
$ strace -Tc ./tstloop
time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
50.85 62.145774 29 2134526 semctl
49.15 60.059067 28 2134527 semget
0.00 0.000088 18 5 old_mmap
0.00 0.000054 18 3 mprotect
0.00 0.000039 20 2 open
0.00 0.000028 14 2 fstat64
0.00 0.000025 13 2 close
0.00 0.000020 20 1 munmap
0.00 0.000018 18 1 read
0.00 0.000018 18 1 uname
0.00 0.000018 18 1 stat64
0.00 0.000014 14 1 1 access
0.00 0.000014 14 1 set_thread_area
0.00 0.000012 12 1 time
0.00 0.000008 8 1 brk
------ ----------- ----------- --------- --------- ----------------
100.00 122.205197 4269075 1 total

when I try
$ strace ./tstloop
semget(1660977153, 2, IPC_CREAT|0777) = 32769 <0.000028>
semctl(32769, 2, IPC_64|GETALL, 0xfeead064) = 0 <0.000029>
.
.
.

Does this output clarifies anything?
# 26  
Old 09-24-2008
Just to be clear, did you try "gprof -p -l" ?


Also, according to this page, you can run "truss -c" on SCO to get similar summary results. If we're lucky, you get per-system-call time, as shown above by ltrace -Tc on Linux. Then you can get what we're really after -- how much time does Linux spend in each system call versus SCO.
# 27  
Old 09-24-2008
SCO has kernel parameter issues with semphores. SHMMAX parameter by default is small. This is a known issue. Here is SCO docset for installing Postgres that discusses it.

Managing Kernel Resources

There are directions for viewing the SHMMAX setting . If it is default, consider raising the value and see if it resolves the shared memory problems you are having.

Otheus -

you are correct - times() uses struct tms not utimes(). That was my bad.
# 28  
Old 09-24-2008
Quote:
Originally Posted by jim mcnamara
SCO has kernel parameter issues with semphores. SHMMAX parameter by default is small. This is a known issue. Here is SCO docset for installing Postgres that discusses it.

Managing Kernel Resources
Jim, Are you thinking that the size of SHMxxx parameters influences the performance?

Migurus,

What do you have set for your Linux shared memory settings? "/sbin/sysctl -a |grep shm". (Ignore errors). Compare those to what is set for SCO (I don't know how to get those).
Login or Register to Ask a Question

Previous Thread | Next Thread

9 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

Semaphore

I was asked to add this piece of code to a c program which I will execute through the shell: for(long i = 0; i < NITER; i++) { sem_wait( &sema); count++; sem_post( &sema); } I didn't get it, which is the critical section ? if it's "count++" how would a thread wake up in order to enter it... (1 Reply)
Discussion started by: uniran
1 Replies

2. Programming

Semaphore

If I create a semaphore and then I fork a number of child processes then all the child process use that same semaphore. Since the process address spaces are different rfom each other then how all the child process are able to access the same semaphore? I understand that semaphore/mutex is at os... (0 Replies)
Discussion started by: rupeshkp728
0 Replies

3. Shell Programming and Scripting

semaphore

Control two exclusively shared resources(semaphore). The two resources are two files. The producer will write even numbers to one file, and odd numbers to another one. The consumer respectively reads from each file until it gets 5 even numbers and 5 odd numbers. Can any one help me with the... (0 Replies)
Discussion started by: gokult
0 Replies

4. Filesystems, Disks and Memory

data from blktrace: read speed V.S. write speed

I analysed disk performance with blktrace and get some data: read: 8,3 4 2141 2.882115217 3342 Q R 195732187 + 32 8,3 4 2142 2.882116411 3342 G R 195732187 + 32 8,3 4 2144 2.882117647 3342 I R 195732187 + 32 8,3 4 2145 ... (1 Reply)
Discussion started by: W.C.C
1 Replies

5. UNIX for Dummies Questions & Answers

semaphore

what is semaphore? can any body explain it in a more simple way than the manual ?? replies appreciated Regards raguram R (7 Replies)
Discussion started by: raguramtgr
7 Replies

6. Shell Programming and Scripting

Semaphore

Hi, I am looking to use a semaphore for the first time in one of my scripts. I am just wondering if there are any simple examples or tutorials around? I am a beginner so the simpler the better :) Thanks -Jaken (2 Replies)
Discussion started by: Jaken
2 Replies

7. Filesystems, Disks and Memory

dmidecode, RAM speed = "Current Speed: Unknown"

Hello, I have a Supermicro server with a P4SCI mother board running Debian Sarge 3.1. This is the "dmidecode" output related to RAM info: RAM speed information is incomplete.. "Current Speed: Unknown", is there anyway/soft to get the speed of installed RAM modules? thanks!! Regards :)... (0 Replies)
Discussion started by: Santi
0 Replies

8. UNIX for Dummies Questions & Answers

Semaphore

Hi, I'm new to UNIX. I need to know what's a semaphore Do reply. Thanks VJ (3 Replies)
Discussion started by: vjsony
3 Replies

9. UNIX for Dummies Questions & Answers

semaphore

hi, is there any command where we can monitor semaphores? (1 Reply)
Discussion started by: yls177
1 Replies
Login or Register to Ask a Question