linux-kernel - Re: [PATCH v2] block: make iolatency avg

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Date:   Wed, 1 Aug 2018 12:46:12 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Dennis Zhou <dennisszhou@...il.com>
Cc:     kbuild-all@...org, Tejun Heo <tj@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, Josef Bacik <jbacik@...com>,
        kernel-team@...com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        "Dennis Zhou (Facebook)" <dennisszhou@...il.com>
Subject: Re: [PATCH v2] block: make iolatency avg_lat exponentially decay

Hi Dennis,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on block/for-next]
[also build test ERROR on next-20180731]
[cannot apply to v4.18-rc7]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Dennis-Zhou/block-make-iolatency-avg_lat-exponentially-decay/20180801-100533
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: i386-randconfig-i1-201830 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   block/blk-iolatency.o: In function `iolatency_check_latencies':
>> block/blk-iolatency.c:511: undefined reference to `__udivdi3'

vim +511 block/blk-iolatency.c

   478	
   479	static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
   480	{
   481		struct blkcg_gq *blkg = lat_to_blkg(iolat);
   482		struct iolatency_grp *parent;
   483		struct child_latency_info *lat_info;
   484		struct blk_rq_stat stat;
   485		unsigned long flags;
   486		int cpu, exp_idx;
   487	
   488		blk_rq_stat_init(&stat);
   489		preempt_disable();
   490		for_each_online_cpu(cpu) {
   491			struct blk_rq_stat *s;
   492			s = per_cpu_ptr(iolat->stats, cpu);
   493			blk_rq_stat_sum(&stat, s);
   494			blk_rq_stat_init(s);
   495		}
   496		preempt_enable();
   497	
   498		parent = blkg_to_lat(blkg->parent);
   499		if (!parent)
   500			return;
   501	
   502		lat_info = &parent->child_lat;
   503	
   504		/*
   505		 * CALC_LOAD takes in a number stored in fixed point representation.
   506		 * Because we are using this for IO time in ns, the values stored
   507		 * are significantly larger than the FIXED_1 denominator (2048).
   508		 * Therefore, rounding errors in the calculation are negligible and
   509		 * can be ignored.
   510		 */
 > 511		exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1,
   512				iolat->cur_win_nsec / BLKIOLATENCY_EXP_BUCKET_SIZE);
   513		CALC_LOAD(iolat->total_lat_avg, iolatency_exp_factors[exp_idx],
   514			  stat.mean);
   515	
   516		/* Everything is ok and we don't need to adjust the scale. */
   517		if (stat.mean <= iolat->min_lat_nsec &&
   518		    atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE)
   519			return;
   520	
   521		/* Somebody beat us to the punch, just bail. */
   522		spin_lock_irqsave(&lat_info->lock, flags);
   523		lat_info->nr_samples -= iolat->nr_samples;
   524		lat_info->nr_samples += stat.nr_samples;
   525		iolat->nr_samples = stat.nr_samples;
   526	
   527		if ((lat_info->last_scale_event >= now ||
   528		    now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME) &&
   529		    lat_info->scale_lat <= iolat->min_lat_nsec)
   530			goto out;
   531	
   532		if (stat.mean <= iolat->min_lat_nsec &&
   533		    stat.nr_samples >= BLKIOLATENCY_MIN_GOOD_SAMPLES) {
   534			if (lat_info->scale_grp == iolat) {
   535				lat_info->last_scale_event = now;
   536				scale_cookie_change(iolat->blkiolat, lat_info, true);
   537			}
   538		} else if (stat.mean > iolat->min_lat_nsec) {
   539			lat_info->last_scale_event = now;
   540			if (!lat_info->scale_grp ||
   541			    lat_info->scale_lat > iolat->min_lat_nsec) {
   542				WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec);
   543				lat_info->scale_grp = iolat;
   544			}
   545			scale_cookie_change(iolat->blkiolat, lat_info, false);
   546		}
   547	out:
   548		spin_unlock_irqrestore(&lat_info->lock, flags);
   549	}
   550	

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