From: Paul Chavent Subject: Re: Constant access (write) time. Date: Mon, 08 Mar 2010 21:17:03 +0100 Message-ID: <4B955B3F.8070004@fnac.net> References: <4B92D10D.8070805@fnac.net> <20100306231327.GI6000@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: tytso@mit.edu Return-path: Received: from smtp1-g21.free.fr ([212.27.42.1]:41993 "EHLO smtp1-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755543Ab0CHUM2 (ORCPT ); Mon, 8 Mar 2010 15:12:28 -0500 In-Reply-To: <20100306231327.GI6000@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hello. Thank you for your reply. I have an intel SSD 2.5 inch X25-M 80GB SATA300. And i have the following log : # /test_ext4 file size duration 58157568 11809470 62773248 10658968 266786304 11514789 287403008 10423548 308327424 13095972 329251840 11036123 350176256 12643903 370792960 9767548 391717376 10987771 411410944 13204409 ^C diff min : 2298627 diff moy : 3971804 diff max : 13204409 1342 iterations major pagefaults : 0 minor pagefaults : 0 Could you give me more detail on your configuration ? Here, more details on mine : # mke2fs -t ext4 -L DATA -O large_file,^has_journal,extent -v /dev/sda3 mke2fs 1.41.9 (22-Aug-2009) fs_types for mke2fs.conf resolution: 'ext4', 'default' Filesystem label=DATA OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) 3670016 inodes, 14653288 blocks 732664 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=0 448 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424 Writing inode tables: done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 37 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override. # dumpe2fs -h /dev/sda3 dumpe2fs 1.41.9 (22-Aug-2009) Filesystem volume name: DATA Last mounted on: Filesystem UUID: 13b72368-2a9e-11df-8a9f-0060c2140392 Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize Filesystem flags: signed_directory_hash Default mount options: (none) Filesystem state: clean Errors behavior: Continue Filesystem OS type: Linux Inode count: 3670016 Block count: 14653288 Reserved block count: 732664 Free blocks: 14409685 Free inodes: 3670005 First block: 0 Block size: 4096 Fragment size: 4096 Reserved GDT blocks: 1020 Blocks per group: 32768 Fragments per group: 32768 Inodes per group: 8192 Inode blocks per group: 512 Flex block group size: 16 Filesystem created: Mon Mar 8 10:33:46 2010 Last mount time: n/a Last write time: Mon Mar 8 10:34:00 2010 Mount count: 0 Maximum mount count: 37 Last checked: Mon Mar 8 10:33:46 2010 Check interval: 15552000 (6 months) Next check after: Sat Sep 4 10:33:46 2010 Lifetime writes: 900 MB Reserved blocks uid: 0 (user root) Reserved blocks gid: 0 (group root) First inode: 11 Inode size: 256 Required extra isize: 28 Desired extra isize: 28 Default directory hash: half_md4 Directory Hash Seed: 13b723f4-2a9e-11df-8a9f-0060c2140392 # mount -t ext4 -o noatime,nodiratime /dev/sda3 /var/data EXT4-fs (sda3): no journal EXT4-fs (sda3): delayed allocation enabled EXT4-fs: file extents enabled EXT4-fs: mballoc enabled EXT4-fs (sda3): mounted filesystem without journal # hdparm -i /dev/sda /dev/sda: hdparm: ioctl 0x304 failed: Inappropriate ioctl for device Model=INTEL SSDSA2MH080G1GC , FwRev=045C8820, SerialNo=CVEM8385003E080DGN Config={ Fixed } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=0 BuffType=(0) unknown, BuffSize=0kB, MaxMultSect=16, MultSect=?1? CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio3 pio4 DMA modes: mdma0 mdma1 mdma2 UDMA modes: udma0 udma1 udma2 AdvancedPM=no WriteCache=enabled Drive conforms to: ATA/ATAPI-7 T13 1532D rev.1: ATA/ATAPI-2 ATA/ATAPI-3 ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7 * current active mode tytso@mit.edu wrote: > On Sat, Mar 06, 2010 at 11:02:53PM +0100, Paul Chavent wrote: >> Hello. >> >> I'm writing a real-time application that have to stream pictures to a SSD. >> >> The pictures are 640x480x1 pnm that are stored in one tar file. I >> have one picture every 100ms. >> >> The problem is that the access (write) time (from a userspace point >> of view) is not constant. I join you a piece of code that reproduce >> the problem. > > What are you seeing/expecting? Here's what I'm getting with the X25-M > Intel SSD: > > file size duration > > diff min : 3666548 > diff moy : 6639261 > diff max : 9429924 > 101 iterations > major pagefaults : 0 > minor pagefaults : 0 > > It's rarely if ever triggering your "suspect write" fprintf. > >> This leads me to ask the following questions : the solution to this >> problem is >> > > If you are seeing something seriously worse, you might want to test > what happens if you write to the SSD directly; it may be the answer is > > (4) Buy a competently engineered SSD. :-) > > - Ted > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > >