Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757615AbZFPEaA (ORCPT ); Tue, 16 Jun 2009 00:30:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750798AbZFPE3v (ORCPT ); Tue, 16 Jun 2009 00:29:51 -0400 Received: from authsmtp00.uchicago.edu ([128.135.249.245]:48956 "EHLO authsmtp00.uchicago.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750791AbZFPE3u (ORCPT ); Tue, 16 Jun 2009 00:29:50 -0400 X-Greylist: delayed 824 seconds by postgrey-1.27 at vger.kernel.org; Tue, 16 Jun 2009 00:29:50 EDT Message-ID: <4A371AED.5080800@uchicago.edu> Date: Tue, 16 Jun 2009 00:09:17 -0400 From: Jake Ellowitz User-Agent: Thunderbird 2.0.0.21 (X11/20090319) MIME-Version: 1.0 To: Wu Fengguang CC: "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , tj@kernel.org, Andrew Morton , Jens Axboe Subject: Re: [Bug #13463] Poor SSD performance References: <20090610063746.GA26773@localhost> <20090611031153.GA7007@localhost> In-Reply-To: <20090611031153.GA7007@localhost> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9077 Lines: 183 Dear Fengguang, Thanks so much for the attention you paid to this problem. I did not want to respond until I got a chance to give the new kernel a shot to see if the bug was still present. It appears not to be -- hdparm and dd both register read speeds between 200 and 220 MB/s as opposed to the 70 to 80 MB/s I was getting with kernel 2.6.29. So, I guess this strange bug has sort of resolved itself. Best, Jake Wu Fengguang wrote: > On Wed, Jun 10, 2009 at 02:37:46PM +0800, Wu Fengguang wrote: > >>> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13463 >>> Subject : Poor SSD performance >>> Submitter : Jake >>> Date : 2009-06-05 17:37 (3 days old) >>> >> Hi Jake, >> >> Could you collect some blktrace data for the dd commands on new/old >> kernels? >> >> dd if=/dev/sda of=/dev/null bs=1M count=1024 iflag=direct >> dd if=/dev/sda of=/dev/null bs=1M count=1024 >> > > I managed to get a SanDisk SSD for testing, and observes that > > - one must increase read_ahead_kb to at least max_sectors_kb or better > "bs=1M" to make a fair comparison > - with increased readahead size, the dd reported throughputs are > 75MB/s vs 77MB/s, while the blktrace reported throughputs are > 75MB/s vs 75MB/s (buffered IO vs direct IO). > > Here are details. > > The dd throughputs are equal for rotational hard disks, but differs > for this SanDisk SSD (with default RA parameters): > > % dd if=/dev/sda of=/dev/null iflag=direct bs=1M count=1024 > 1073741824 bytes (1.1 GB) copied, 13.905 s, 77.2 MB/s > 1073741824 bytes (1.1 GB) copied, 13.9029 s, 77.2 MB/s > > % dd if=/dev/sda of=/dev/null bs=1M count=1024 > 1073741824 bytes (1.1 GB) copied, 14.7294 s, 72.9 MB/s > 1073741824 bytes (1.1 GB) copied, 14.8647 s, 72.2 MB/s > > Here is the blktrace summary: > > dd dd-direct > -------------------------------------------------------------------------------------- > CPU0 (sda): | CPU0 (sda): > Reads Queued: 9,888, 39,552KiB | Reads Queued: 84, 43,008KiB > Read Dispatches: 302, 38,588KiB | Read Dispatches: 84, 43,008KiB > Reads Requeued: 0 | Reads Requeued: 0 > Reads Completed: 337, 44,600KiB | Reads Completed: 83, 42,496KiB > Read Merges: 9,574, 38,296KiB | Read Merges: 0, 0KiB > Read depth: 2 | Read depth: 2 > IO unplugs: 313 | IO unplugs: 42 > CPU1 (sda): | CPU1 (sda): > Reads Queued: 11,840, 47,360KiB | Reads Queued: 96, 49,152KiB > Read Dispatches: 372, 48,196KiB | Read Dispatches: 96, 49,152KiB > Reads Requeued: 0 | Reads Requeued: 0 > Reads Completed: 337, 42,312KiB | Reads Completed: 96, 49,152KiB > Read Merges: 11,479, 45,916KiB | Read Merges: 0, 0KiB > Read depth: 2 | Read depth: 2 > IO unplugs: 372 | IO unplugs: 48 > | > Total (sda): | Total (sda): > Reads Queued: 21,728, 86,912KiB | Reads Queued: 180, 92,160KiB > Read Dispatches: 674, 86,784KiB | Read Dispatches: 180, 92,160KiB > Reads Requeued: 0 | Reads Requeued: 0 > Reads Completed: 674, 86,912KiB | Reads Completed: 179, 91,648KiB > Read Merges: 21,053, 84,212KiB | Read Merges: 0, 0KiB > IO unplugs: 685 | IO unplugs: 90 > | > Throughput (R/W): 69,977KiB/s / 0KiB/s | Throughput (R/W): 75,368KiB/s / 0KiB/s > Events (sda): 46,804 entries | Events (sda): 1,158 entries > > > Another obvious difference is IO size. > One is read_ahead_kb=128K, another is max_sectors_kb=512K: > > dd: > 8,0 0 13497 0.804939305 0 C R 782592 + 256 [0] > 8,0 0 13498 0.806713692 0 C R 782848 + 256 [0] > 8,0 1 16275 0.808488708 0 C R 783104 + 256 [0] > 8,0 0 13567 0.810261350 0 C R 783360 + 256 [0] > 8,0 0 13636 0.812036226 0 C R 783616 + 256 [0] > 8,0 1 16344 0.813806353 0 C R 783872 + 256 [0] > 8,0 1 16413 0.815578436 0 C R 784128 + 256 [0] > 8,0 0 13705 0.817347935 0 C R 784384 + 256 [0] > > dd-direct: > 8,0 0 428 0.998831975 0 C R 357376 + 1024 [0] > 8,0 1 514 1.005683404 0 C R 358400 + 1024 [0] > 8,0 1 515 1.012402554 0 C R 359424 + 1024 [0] > 8,0 0 440 1.019303850 0 C R 360448 + 1024 [0] > 8,0 1 526 1.026024048 0 C R 361472 + 1024 [0] > 8,0 1 538 1.032875967 0 C R 362496 + 1024 [0] > 8,0 0 441 1.039595815 0 C R 363520 + 1024 [0] > > The non-direct dd throughput can improve with 512K and 1M readahead size, > but still a bit slower than the direct dd case: > 1073741824 bytes (1.1 GB) copied, 14.1619 s, 75.8 MB/s > 1073741824 bytes (1.1 GB) copied, 14.1517 s, 75.9 MB/s > > dd-512k dd-direct2 > ------------------------------------------------------------------------------------- > Total (sda): | Total (sda): > Reads Queued: 23,808, 95,232KiB | Reads Queued: 178, 91,136KiB > Read Dispatches: 215, 95,232KiB | Read Dispatches: 178, 91,136KiB > Reads Requeued: 0 | Reads Requeued: 0 > Reads Completed: 215, 95,232KiB | Reads Completed: 177, 90,624KiB > Read Merges: 23,593, 94,372KiB | Read Merges: 0, 0KiB > IO unplugs: 236 | IO unplugs: 89 > | > Throughput (R/W): 75,222KiB/s / 0KiB/s | Throughput (R/W): 75,520KiB/s / 0KiB/s > Events (sda): 48,687 entries | Events (sda): 1,145 entries > > Interestingly, the throughput reported by blktrace is almost the same, > whereas the dd report favors the dd-direct case. > > More parameters. > > [ 10.137350] scsi 3:0:0:0: Direct-Access ATA SanDisk SSD SATA 1.13 PQ: 0 ANSI: 5 > [ 10.147137] sd 3:0:0:0: [sda] 61500000 512-byte hardware sectors: (31.4 GB/29.3 GiB) > [ 10.155060] sd 3:0:0:0: [sda] Write Protect is off > [ 10.159922] sd 3:0:0:0: [sda] Mode Sense: 00 3a 00 00 > [ 10.165179] sd 3:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA > [ 10.174994] sda: > > > /dev/sda: > > Model=SanDisk SSD SATA 5000 2.5 , FwRev=1.13 , SerialNo= 81402200246 > Config={ Fixed } > RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 > BuffType=unknown, BuffSize=0kB, MaxMultSect=1, MultSect=?1? > CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=61500000 > IORDY=yes, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} > PIO modes: pio0 pio1 pio2 pio3 pio4 > DMA modes: mdma0 mdma1 mdma2 > UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5 > AdvancedPM=yes: disabled (255) WriteCache=disabled > Drive conforms to: unknown: ATA/ATAPI-2,3,4,5,6,7 > > * signifies the current active mode > > > /sys/block/sda/queue/nr_requests:128 > /sys/block/sda/queue/read_ahead_kb:128 > /sys/block/sda/queue/max_hw_sectors_kb:32767 > /sys/block/sda/queue/max_sectors_kb:512 > /sys/block/sda/queue/scheduler:noop [cfq] > /sys/block/sda/queue/hw_sector_size:512 > /sys/block/sda/queue/rotational:1 > /sys/block/sda/queue/nomerges:0 > /sys/block/sda/queue/rq_affinity:0 > /sys/block/sda/queue/iostats:1 > /sys/block/sda/queue/iosched/quantum:4 > /sys/block/sda/queue/iosched/fifo_expire_sync:124 > /sys/block/sda/queue/iosched/fifo_expire_async:248 > /sys/block/sda/queue/iosched/back_seek_max:16384 > /sys/block/sda/queue/iosched/back_seek_penalty:2 > /sys/block/sda/queue/iosched/slice_sync:100 > /sys/block/sda/queue/iosched/slice_async:40 > /sys/block/sda/queue/iosched/slice_async_rq:2 > /sys/block/sda/queue/iosched/slice_idle:8 > > Thanks, > Fengguang > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/