Re: [PATCH tip/locking/core v10 5/7] locking/pvqspinlock: Collect slowpath lock statistics

[Waiman Long]

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On 11/23/2015 04:51 AM, Peter Zijlstra wrote:
> On Mon, Nov 09, 2015 at 07:09:25PM -0500, Waiman Long wrote:
> > +static ssize_t qstat_read(struct file *file, char __user *user_buf,
> > +			  size_t count, loff_t *ppos)
> > +{
> > +	char buf[64];
> > +	int cpu, counter, len;
> > +	u64 stat = 0, kicks = 0;
> > +
> > +	/*
> > +	 * Get the counter ID stored in file->f_inode->i_private
> > +	 */
> > +	if (!file->f_inode) {
> > +		WARN_ON_ONCE(1);
> > +		return -EBADF;
> > +	}
> > +	counter = (long)(file->f_inode->i_private);
> > +
> > +	if (counter>= qstat_num)
> > +		return -EBADF;
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		stat += per_cpu(qstats[counter], cpu);
> > +		/*
> > +		 * Need to sum additional counter for some of them
> > +		 */
> > +		switch (counter) {
> > +
> > +		case qstat_pv_latency_kick:
> > +		case qstat_pv_hash_hops:
> > +			kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
> > +			break;
> > +
> > +		case qstat_pv_latency_wake:
> > +			kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
> > +			break;
> > +		}
> > +	}
> > +
> > +	if (counter == qstat_pv_hash_hops) {
> > +		/*
> > +		 * Return a X.XX decimal number
> > +		 */
> > +		len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
> > +			       stat/kicks, ((stat%kicks)*100 + kicks/2)/kicks);
> > +	} else {
> > +		/*
> > +		 * Round to the nearest ns
> > +		 */
> > +		if ((counter == qstat_pv_latency_kick) ||
> > +		    (counter == qstat_pv_latency_wake))
> > +			stat = kicks ? (stat + kicks/2)/kicks : 0;
> > +		len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
> > +	}
> > +
> > +	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
> > +}
> That doesn't work on 32bit.

Thanks for catching that. I should not use u64 for the stat and kick 
variables. I have attached the fixed version of the patch that should 
work on 32-bit.

Cheers,
Longman