forked from Minki/linux
md/raid5: per hash value and exclusive wait_for_stripe
I noticed heavy spin lock contention at get_active_stripe() with fsmark multiple thread write workloads. Here is how this hot contention comes from. We have limited stripes, and it's a multiple thread write workload. Hence, those stripes will be taken soon, which puts later processes to sleep for waiting free stripes. When enough stripes(>= 1/4 total stripes) are released, all process are woken, trying to get the lock. But there is one only being able to get this lock for each hash lock, making other processes spinning out there for acquiring the lock. Thus, it's effectiveless to wakeup all processes and let them battle for a lock that permits one to access only each time. Instead, we could make it be a exclusive wake up: wake up one process only. That avoids the heavy spin lock contention naturally. To do the exclusive wake up, we've to split wait_for_stripe into multiple wait queues, to make it per hash value, just like the hash lock. Here are some test results I have got with this patch applied(all test run 3 times): `fsmark.files_per_sec' ===================== next-20150317 this patch ------------------------- ------------------------- metric_value ±stddev metric_value ±stddev change testbox/benchmark/testcase-params ------------------------- ------------------------- -------- ------------------------------ 25.600 ±0.0 92.700 ±2.5 262.1% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-btrfs-4M-30G-fsyncBeforeClose 25.600 ±0.0 77.800 ±0.6 203.9% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-btrfs-4M-30G-fsyncBeforeClose 32.000 ±0.0 93.800 ±1.7 193.1% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-ext4-4M-30G-fsyncBeforeClose 32.000 ±0.0 81.233 ±1.7 153.9% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-ext4-4M-30G-fsyncBeforeClose 48.800 ±14.5 99.667 ±2.0 104.2% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-xfs-4M-30G-fsyncBeforeClose 6.400 ±0.0 12.800 ±0.0 100.0% ivb44/fsmark/1x-64t-3HDD-RAID5-btrfs-4M-40G-fsyncBeforeClose 63.133 ±8.2 82.800 ±0.7 31.2% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-xfs-4M-30G-fsyncBeforeClose 245.067 ±0.7 306.567 ±7.9 25.1% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-f2fs-4M-30G-fsyncBeforeClose 17.533 ±0.3 21.000 ±0.8 19.8% ivb44/fsmark/1x-1t-3HDD-RAID5-xfs-4M-40G-fsyncBeforeClose 188.167 ±1.9 215.033 ±3.1 14.3% ivb44/fsmark/1x-1t-4BRD_12G-RAID5-btrfs-4M-30G-NoSync 254.500 ±1.8 290.733 ±2.4 14.2% ivb44/fsmark/1x-1t-9BRD_6G-RAID5-btrfs-4M-30G-NoSync `time.system_time' ===================== next-20150317 this patch ------------------------- ------------------------- metric_value ±stddev metric_value ±stddev change testbox/benchmark/testcase-params ------------------------- ------------------------- -------- ------------------------------ 7235.603 ±1.2 185.163 ±1.9 -97.4% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-btrfs-4M-30G-fsyncBeforeClose 7666.883 ±2.9 202.750 ±1.0 -97.4% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-btrfs-4M-30G-fsyncBeforeClose 14567.893 ±0.7 421.230 ±0.4 -97.1% ivb44/fsmark/1x-64t-3HDD-RAID5-btrfs-4M-40G-fsyncBeforeClose 3697.667 ±14.0 148.190 ±1.7 -96.0% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-xfs-4M-30G-fsyncBeforeClose 5572.867 ±3.8 310.717 ±1.4 -94.4% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-ext4-4M-30G-fsyncBeforeClose 5565.050 ±0.5 313.277 ±1.5 -94.4% ivb44/fsmark/1x-64t-4BRD_12G-RAID5-ext4-4M-30G-fsyncBeforeClose 2420.707 ±17.1 171.043 ±2.7 -92.9% ivb44/fsmark/1x-64t-9BRD_6G-RAID5-xfs-4M-30G-fsyncBeforeClose 3743.300 ±4.6 379.827 ±3.5 -89.9% ivb44/fsmark/1x-64t-3HDD-RAID5-ext4-4M-40G-fsyncBeforeClose 3308.687 ±6.3 363.050 ±2.0 -89.0% ivb44/fsmark/1x-64t-3HDD-RAID5-xfs-4M-40G-fsyncBeforeClose Where, 1x: where 'x' means iterations or loop, corresponding to the 'L' option of fsmark 1t, 64t: where 't' means thread 4M: means the single file size, corresponding to the '-s' option of fsmark 40G, 30G, 120G: means the total test size 4BRD_12G: BRD is the ramdisk, where '4' means 4 ramdisk, and where '12G' means the size of one ramdisk. So, it would be 48G in total. And we made a raid on those ramdisk As you can see, though there are no much performance gain for hard disk workload, the system time is dropped heavily, up to 97%. And as expected, the performance increased a lot, up to 260%, for fast device(ram disk). v2: use bits instead of array to note down wait queue need to wake up. Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com> Signed-off-by: NeilBrown <neilb@suse.de>
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@ -344,7 +344,8 @@ static void release_inactive_stripe_list(struct r5conf *conf,
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int hash)
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{
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int size;
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bool do_wakeup = false;
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unsigned long do_wakeup = 0;
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int i = 0;
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unsigned long flags;
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if (hash == NR_STRIPE_HASH_LOCKS) {
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@ -365,15 +366,19 @@ static void release_inactive_stripe_list(struct r5conf *conf,
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!list_empty(list))
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atomic_dec(&conf->empty_inactive_list_nr);
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list_splice_tail_init(list, conf->inactive_list + hash);
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do_wakeup = true;
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do_wakeup |= 1 << hash;
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spin_unlock_irqrestore(conf->hash_locks + hash, flags);
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}
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size--;
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hash--;
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}
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for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++) {
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if (do_wakeup & (1 << i))
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wake_up(&conf->wait_for_stripe[i]);
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}
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if (do_wakeup) {
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wake_up(&conf->wait_for_stripe);
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if (atomic_read(&conf->active_stripes) == 0)
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wake_up(&conf->wait_for_quiescent);
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if (conf->retry_read_aligned)
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@ -686,14 +691,15 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
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if (!sh) {
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set_bit(R5_INACTIVE_BLOCKED,
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&conf->cache_state);
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wait_event_lock_irq(
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conf->wait_for_stripe,
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wait_event_exclusive_cmd(
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conf->wait_for_stripe[hash],
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!list_empty(conf->inactive_list + hash) &&
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(atomic_read(&conf->active_stripes)
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< (conf->max_nr_stripes * 3 / 4)
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|| !test_bit(R5_INACTIVE_BLOCKED,
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&conf->cache_state)),
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*(conf->hash_locks + hash));
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spin_unlock_irq(conf->hash_locks + hash),
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spin_lock_irq(conf->hash_locks + hash));
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clear_bit(R5_INACTIVE_BLOCKED,
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&conf->cache_state);
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} else {
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@ -718,6 +724,9 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
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}
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} while (sh == NULL);
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if (!list_empty(conf->inactive_list + hash))
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wake_up(&conf->wait_for_stripe[hash]);
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spin_unlock_irq(conf->hash_locks + hash);
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return sh;
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}
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@ -2179,7 +2188,7 @@ static int resize_stripes(struct r5conf *conf, int newsize)
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cnt = 0;
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list_for_each_entry(nsh, &newstripes, lru) {
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lock_device_hash_lock(conf, hash);
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wait_event_cmd(conf->wait_for_stripe,
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wait_event_exclusive_cmd(conf->wait_for_stripe[hash],
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!list_empty(conf->inactive_list + hash),
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unlock_device_hash_lock(conf, hash),
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lock_device_hash_lock(conf, hash));
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@ -6436,7 +6445,9 @@ static struct r5conf *setup_conf(struct mddev *mddev)
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spin_lock_init(&conf->device_lock);
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seqcount_init(&conf->gen_lock);
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init_waitqueue_head(&conf->wait_for_quiescent);
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init_waitqueue_head(&conf->wait_for_stripe);
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for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++) {
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init_waitqueue_head(&conf->wait_for_stripe[i]);
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}
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init_waitqueue_head(&conf->wait_for_overlap);
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INIT_LIST_HEAD(&conf->handle_list);
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INIT_LIST_HEAD(&conf->hold_list);
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@ -512,7 +512,7 @@ struct r5conf {
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atomic_t empty_inactive_list_nr;
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struct llist_head released_stripes;
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wait_queue_head_t wait_for_quiescent;
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wait_queue_head_t wait_for_stripe;
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wait_queue_head_t wait_for_stripe[NR_STRIPE_HASH_LOCKS];
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wait_queue_head_t wait_for_overlap;
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unsigned long cache_state;
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#define R5_INACTIVE_BLOCKED 1 /* release of inactive stripes blocked,
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