Jay Lan wrote:
>Shailabh Nagar wrote:
>  
>>Andrew Morton wrote:
>> 
>>    
>>>You see the problem - if one userspace package wants the tgid-stats and
>>>another concurrently-running one does now, what do we do?  Just leave it
>>>enabled and run a bit slower?
>>>
>>>If so, how much slower?  Your changelog says some potential users don't
>>>need the tgid-stats, but so what?  I assume this patch is a performance
>>>thing?  If so, has it been quantified?
>>>   
>>>      
>>Here are some results from running a simple program (source below) that does
>>10 iterations of creating and then destroying 1000 threads. On the side, another utility
>>kept reading the pid (+tgid if present) stats from exiting tasks.
>> 
>>    
>
>I ran my testing using the same program posted by Shalilabh attached in his
>posting.
>
>System: SGI a350, a two cpus IA64 machine.
>Kernel:  2.6.17-rc3 + delay-acct-taskstats patch set
>       + tgid-disable_patch_shailabh + exit race patch_balbir +
>csa_patch_jlan
>
>I also modified the Decumentation/accounting/getdelay.c:
>   - it repeatedly does recv() to retrieve data from kernel
>   - instead of using printf() to display data received, i simply write
>it to
>     disk as it would be for an accounting daemon. Note that currently
>both the
>     BSD (or GNU) accounting and the CSA writes accounting data from kernel.
>     As an effort of moving accounting system to userspace, the raw data
>needs
>     to be written to a raw file first before further processing.
>
>In Shailabh's testing, he ran his 'mkthreads' 10 iterations of creating and
>distroying 1000 threads.  I had to increase my test to 5000 iterations
>in order
>to receive meaningful data: 'mkthreads 1000 5000'.
>
>I used Shailabh's per-tgid-disable patch to run my tests with per-tgid
>enabled and disabled. I used 'sa' command of 'acct' package to report
>results of 5 runs of 'mkthreads 1000 5000'.
>
>  
>>	Yes	No	Ovhd
>>user	0.14	0.15	-6%
>>system	1.61	1.54	+5%
>>elapsed	2.01	1.94	+3%
>>
>>Yes = tgid stats printed on exit
>>No = not printed
>>Ovhd = (Yes-No)/No * 100
>> 
>>    
>
>Here are test results:
>
>             Yes      No     Ovhd
>user         1.77    0.44    302.27%
>system       0.06    0.06      0.00%
>  

Please swap "user" label with "system" label. Sorry.

Also i forgot to attach the two files.

- jay

>elapsed    794.60  316.40    151.14%
>
>Also, the results of five runs of per-tgid-disabled were very
>consistent (3 runs of 0,44 seconds and 2 runs of 0.45), while
>those of per-tgid-enabled varies (1.56, 1.99, 1.54, 2.21, 1.57).
>
>The impact of per-tgid stats is too significant to ignore for
>those who do not need the per-tgid stats data.
>
>Another observation that i considered bad news is that all
>10 runs produced 1 to 5 recv() error with errno=105 (ENOBUF).
>
>Here I attach my csa_taskstats patch and my modified version of
>exit_recv.c.
>
>Regards,
> - jay
>
>
>  
>>So even in this extreme case where the per-tgid stats are indeed
>>half of the total data, the overhead is not very significant.
>>
>>As pointed out earlier, more representative cases are
>>- single threaded apps (e.g. make -jX) where the current
>>taskstats interface already optimizes by not sending redundant per-tgid stats, or
>>- server-type multithreaded apps where the exits are going to be relatively infrequent (due to
>>reuse of thread pools) so the extra per-tgid output is not going to have much impact.
>>
>>I'd suggest we drop the idea of including this patch until we have data showing that
>>the overhead is an issue.
>>
>>--Shailabh
>>
>>
>>
>>#include <stdio.h>
>>#include <stdlib.h>
>>#include <sys/types.h>
>>#include <unistd.h>
>>#include <pthread.h>
>>
>>int n;
>>
>>void *slow_exit(void *arg)
>>{
>>	int i = (int) arg;
>>	usleep((n-i)*2);
>>}
>>
>>int main(int argc, char *argv[])
>>{
>>	int i,rc, rep;
>>	pthread_t *ppthread;
>>	
>>	n = 5 ;
>>	if (argc > 1)
>>		n = atoi(argv[1]);
>>
>>	rep = 10;
>>	if (argc > 2)
>>		rep = atoi(argv[2]);
>>
>>	ppthread = malloc(n * sizeof(pthread_t));
>>	if (ppthread == NULL) {
>>		printf("Memory allocation failure\n");
>>		exit(-1);
>>	}
>>
>>	while (rep) {
>>		for (i=0; i<n; i++) {
>>			rc = pthread_create(&ppthread[i], NULL,
>>					    slow_exit, (void *)i);
>>			if (rc) {
>>				printf("Error creating thread %d\n", i);
>>				exit(-1);
>>			}
>>		}
>>		for (i=0; i<n; i++) {
>>			rc = pthread_join(ppthread[i], NULL);
>>			if (rc) {
>>				printf("Error joining thread %d\n", i);
>>				exit(-1);
>>			}
>>		}
>>		rep--;
>>	}
>>}
>>
>>
>>
>> 
>>    
>
>