Re: [PATCH] delay-accounting: Re-implement -c for getdelays.c to report information on a target command

[Balbir Singh <balbir@linux.vnet.ibm.com>]

On Tuesday 19 January 2010 11:30 PM, Mel Gorman wrote:
> Task delay-accounting was identified as one means of determining how long
> a process spends in congestion_wait() without adding new statistics. For
> example, if the workload should not be doing IO, delay-accounting could
> reveal how long it was spending in unexpected IO or delays. Unfortunately,
> on closer examination it was clear that getdelays does not act as documented.
> 
> Commit a3baf649 added Documentation/accounting/getdelays.c with a -c switch
> that was documented to fork/exec a child and report statistics on it but for
> reasons that are unclear to me, commit 9e06d3f9 deleted support for this

That is an oversight and not intentional. I've not gotten around to
reimplementing the -c option due to lack for people asking for it.

> switch but did not update the documentation. It might be an oversight or
> it might be because the control flow of the program meant that accounting
> information would be printed once early in the lifetime of the program
> making it of limited use.
> 
> This patch reimplements -c for getdelays.c to act as documented. Unlike the
> original version, it waits until the command completes before printing any
> information on it. An example of it being used looks like
> 

Looks good, could you please keep the original sign-offs as well?

> $ ./getdelays -d -c find /home/mel -name mel
> print delayacct stats ON
> /home/mel
> /home/mel/.notes-wine/drive_c/windows/profiles/mel
> /home/mel/.wine/drive_c/windows/profiles/mel
> /home/mel/git-configs/dot.kde/share/apps/konqueror/home/mel
> PID	5923
> 
> CPU             count     real total  virtual total    delay total
>                 42779     5051232096     5164722692      564207988
> IO              count    delay total
>                 41727    97804147758
> SWAP            count    delay total
>                     0              0
> RECLAIM         count    delay total
>                     0              0
> 
> It's not clear how or if this subsystem is being maintained. If the
> authors agree on it but do not pick it up for merging, I'll go bug
> Andrew with it.
> 

I am maintaining it, please do let me know if you have an issue with the
subsystem or utilities.

> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> --- 
>  Documentation/accounting/getdelays.c |   37 +++++++++++++++++++++++++++++++++--
>  1 file changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
> index 6e25c26..c6648bc 100644
> --- a/Documentation/accounting/getdelays.c
> +++ b/Documentation/accounting/getdelays.c
> @@ -21,6 +21,7 @@
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <sys/socket.h>
> +#include <sys/wait.h>
>  #include <signal.h>
> 
>  #include <linux/genetlink.h>
> @@ -266,11 +267,13 @@ int main(int argc, char *argv[])
>  	int containerset = 0;
>  	char containerpath[1024];
>  	int cfd = 0;
> +	int forking = 0;
> +	sigset_t sigset;
> 
>  	struct msgtemplate msg;
> 
> -	while (1) {
> -		c = getopt(argc, argv, "qdiw:r:m:t:p:vlC:");
> +	while (!forking) {
> +		c = getopt(argc, argv, "qdiw:r:m:t:p:vlC:c:");
>  		if (c < 0)
>  			break;
> 
> @@ -319,6 +322,27 @@ int main(int argc, char *argv[])
>  				err(1, "Invalid pid\n");
>  			cmd_type = TASKSTATS_CMD_ATTR_PID;
>  			break;
> +		case 'c':
> +
> +			/* Block SIGCHLD for sigwait() later */
> +			if (sigemptyset(&sigset) == -1)
> +				err(1, "Failed to empty sigset");
> +			if (sigaddset(&sigset, SIGCHLD))
> +				err(1, "Failed to set sigchld in sigset");
> +			sigprocmask(SIG_BLOCK, &sigset, NULL);
> +
> +			/* fork/exec a child */
> +			tid = fork();
> +			if (tid < 0)
> +				err(1, "Fork failed\n");
> +			if (tid == 0)
> +				if (execvp(argv[optind - 1], &argv[optind - 1]) < 0)
> +					exit(-1);
> +
> +			/* Set the command type and avoid further processing */
> +			cmd_type = TASKSTATS_CMD_ATTR_PID;
> +			forking = 1;
> +			break;
>  		case 'v':
>  			printf("debug on\n");
>  			dbg = 1;
> @@ -370,6 +394,15 @@ int main(int argc, char *argv[])
>  		goto err;
>  	}
> 
> +	/*
> +	 * If we forked a child, wait for it to exit. Cannot use waitpid()
> +	 * as all the delicious data would be reaped as part of the wait 
> +	 */
> +	if (tid && forking) {
> +		int sig_received;
> +		sigwait(&sigset, &sig_received);
> +	}
> +
>  	if (tid) {
>  		rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
>  			      cmd_type, &tid, sizeof(__u32));