From 8b3e6cdc53b7f29f7026955d6cb6902a49322a15 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Mon, 28 Apr 2008 02:15:53 -0700 Subject: md: introduce get_priority_stripe() to improve raid456 write performance Improve write performance by preventing the delayed_list from dumping all its stripes onto the handle_list in one shot. Delayed stripes are now further delayed by being held on the 'hold_list'. The 'hold_list' is bypassed when: * a STRIPE_IO_STARTED stripe is found at the head of 'handle_list' * 'handle_list' is empty and i/o is being done to satisfy full stripe-width write requests * 'bypass_count' is less than 'bypass_threshold'. By default the threshold is 1, i.e. every other stripe handled is a preread stripe provided the top two conditions are false. Benchmark data: System: 2x Xeon 5150, 4x SATA, mem=1GB Baseline: 2.6.24-rc7 Configuration: mdadm --create /dev/md0 /dev/sd[b-e] -n 4 -l 5 --assume-clean Test1: dd if=/dev/zero of=/dev/md0 bs=1024k count=2048 * patched: +33% (stripe_cache_size = 256), +25% (stripe_cache_size = 512) Test2: tiobench --size 2048 --numruns 5 --block 4096 --block 131072 (XFS) * patched: +13% * patched + preread_bypass_threshold = 0: +37% Changes since v1: * reduce bypass_threshold from (chunk_size / sectors_per_chunk) to (1) and make it configurable. This defaults to fairness and modest performance gains out of the box. Changes since v2: * [neilb@suse.de]: kill STRIPE_PRIO_HI and preread_needed as they are not necessary, the important change was clearing STRIPE_DELAYED in add_stripe_bio and this has been moved out to make_request for the hang fix. * [neilb@suse.de]: simplify get_priority_stripe * [dan.j.williams@intel.com]: reset the bypass_count when ->hold_list is sampled empty (+11%) * [dan.j.williams@intel.com]: decrement the bypass_count at the detection of stripes being naturally promoted off of hold_list +2%. Note, resetting bypass_count instead of decrementing on these events yields +4% but that is probably too aggressive. Changes since v3: * cosmetic fixups Tested-by: James W. Laferriere Signed-off-by: Dan Williams Signed-off-by: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/raid/raid5.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/linux/raid') diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h index 93678f57ccbe..f0827d31ae6f 100644 --- a/include/linux/raid/raid5.h +++ b/include/linux/raid/raid5.h @@ -252,6 +252,8 @@ struct r6_state { #define STRIPE_EXPANDING 9 #define STRIPE_EXPAND_SOURCE 10 #define STRIPE_EXPAND_READY 11 +#define STRIPE_IO_STARTED 12 /* do not count towards 'bypass_count' */ +#define STRIPE_FULL_WRITE 13 /* all blocks are set to be overwritten */ /* * Operations flags (in issue order) */ @@ -316,12 +318,17 @@ struct raid5_private_data { int previous_raid_disks; struct list_head handle_list; /* stripes needing handling */ + struct list_head hold_list; /* preread ready stripes */ struct list_head delayed_list; /* stripes that have plugged requests */ struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */ struct bio *retry_read_aligned; /* currently retrying aligned bios */ struct bio *retry_read_aligned_list; /* aligned bios retry list */ atomic_t preread_active_stripes; /* stripes with scheduled io */ atomic_t active_aligned_reads; + atomic_t pending_full_writes; /* full write backlog */ + int bypass_count; /* bypassed prereads */ + int bypass_threshold; /* preread nice */ + struct list_head *last_hold; /* detect hold_list promotions */ atomic_t reshape_stripes; /* stripes with pending writes for reshape */ /* unfortunately we need two cache names as we temporarily have -- cgit v1.2.2