linux-kernel - Re: [PATCH] distinct tgid/tid I/O statistics

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Date:	Mon, 19 May 2008 20:33:11 +0200
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	balbir@...ux.vnet.ibm.com
CC:	Shailabh Nagar <nagar@...son.ibm.com>,
	Mark Seger <Mark.Seger@...com>, Jes Sorensen <jes@....com>,
	Chris Sturtivant <csturtiv@....com>, Tony Ernst <tee@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] distinct tgid/tid I/O statistics

Balbir Singh wrote:
>> +
>> +    if (!whole) {
>> +#ifdef CONFIG_TASK_XACCT
> 
> Can't we abstract this into a function for ease?

Maybe:

#ifdef CONFIG_TASK_XACCT
#define _task_xacct 1
#else
#define _task_xacct 0
#endif

and:

rchar = __task_xacct ? task->rchar : 0;
wchar = __task_xacct ? task->wchar : 0;
syscr = __task_xacct ? task->syscr : 0;
syscw = __task_xacct ? task->syscw : 0;

But it's very ugly anyway. It seems a similar problem has been raised
here:

http://lkml.org/lkml/2008/5/17/154

Apparently with no solution.

> 
>> +        rchar = task->rchar;
>> +        wchar = task->wchar;
>> +        syscr = task->syscr;
>> +        syscw = task->syscw;
>> +#endif
>> +        memcpy(&ioac, &task->ioac, sizeof(ioac));
>> +    } else {
>> +        rchar = wchar = syscr = syscw = 0;
>> +        memset(&ioac, 0, sizeof(ioac));
>> +        rcu_read_lock();
>> +        if (lock_task_sighand(task, &flags)) {
> 
> If lock(), what happens otherwise?
> 

mmmh... we must surely move the threads stats accounting code out of
the if statement. OK, I'll post a new patch soon.

Thanks,
-Andrea

>> +        struct signal_struct *sig = task->signal;
>> +        struct task_struct *t = task;
>> +
>> +            do {
>> +#ifdef CONFIG_TASK_XACCT
>> +                rchar += t->rchar;
>> +                wchar += t->wchar;
>> +                syscr += t->syscr;
>> +                syscw += t->syscw;
>> +#endif
>> +                ioac.read_bytes += t->ioac.read_bytes;
>> +                ioac.write_bytes += t->ioac.write_bytes;
>> +                ioac.cancelled_write_bytes +=
>> +                        t->ioac.cancelled_write_bytes;
>> +                t = next_thread(t);
>> +            } while (t != task);
>> +
>> +#ifdef CONFIG_TASK_XACCT
>> +            rchar += sig->rchar;
>> +            wchar += sig->wchar;
>> +            syscr += sig->syscr;
>> +            syscw += sig->syscw;
>> +#endif
>> +            ioac.read_bytes += sig->ioac.read_bytes;
>> +            ioac.write_bytes += sig->ioac.write_bytes;
>> +            ioac.cancelled_write_bytes +=
>> +                    sig->ioac.cancelled_write_bytes;
>> +
>> +            unlock_task_sighand(task, &flags);
>> +        }
>> +        rcu_read_unlock();
>> +    }
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