Messages in this thread | | | Date | Thu, 18 Mar 2004 10:48:59 -0800 (PST) | From | markw@osdl ... | Subject | Re: 2.6.4-mm2 |
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On 18 Mar, Andrew Morton wrote: > markw@osdl.org wrote: >> >> Sorry I'm falling behind... I see about a 10% decrease in throughput >> with our dbt2 workload when comparing 2.6.4-mm2 to 2.6.3. I'm wondering >> if this might be a result of the changes to the pagecache, radix-tree >> and writeback code since you mentioned it could affect i/o scheduling in >> 2.6.4-mm1. > > Could be. Have you run tests without LVM in the picture?
No I haven't and I'm hesitant to. I have 52 single drives in one volume and 14 single drives the other. Because it's PostgreSQL, my options are to either run on a single drive (and not be able to drive the system as hard) or to reconfigure my drives using hardware raid. I could do the latter if you think it'll help. It's just a bit time consuming.
>> PostgreSQL is using 8KB blocks and the characteristics of the i/o should >> be that one lvm2 volume is experiencing mostly sequential writes, while >> another has random reading and writing. Both these volumes are using >> ext2. I'll summarize the throughput results here, with the lvm2 stripe >> width varying across the columns: >> >> kernel 16 kb 32 kb 64 kb 128 kb 256 kb 512 kb >> 2.6.3 2308 2335 2348 2334 >> 2.6.4-mm2 2028 2048 2074 2096 2082 2078 >> >> Here's a page with links to profile, oprofile, etc of each result: >> http://developer.osdl.org/markw/linux/2.6-pagecache.html >> >> Comparing one pair of readprofile results, I find it curious that >> dm_table_unplug_all and dm_table_any_congested show up near the top of a >> 2.6.4-mm2 profile when they haven't shown up before in 2.6.3. > > 14015190 poll_idle 241641.2069 > 175162 generic_unplug_device 1317.0075 > 165480 __copy_from_user_ll 1272.9231 > 161151 __copy_to_user_ll 1342.9250 > 152106 schedule 85.0705 > 142395 DAC960_LP_InterruptHandler 761.4706 > 113677 dm_table_unplug_all 1386.3049 > 65420 __make_request 45.5571 > 64832 dm_table_any_congested 697.1183 > 37913 try_to_wake_up 32.2939 > > That's broken. How many disks are involve in the DM stack? > > The relevant code was reworked subsequent to 2.6.4-mm2. Maybe we fixed > this, but I cannot immediately explain what you're seeing here.
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