Hi all,
I was working in one application that requires heavy disk
writes, I noticed some inconsistencies in the write timing.
We are using raw reads to bypass filesystem overhead.
Firstly i tried open("/dev/hda",O_RDWR) i.e without O_DIRECT option.
I saw that after some writes 1 write took too much time.
the results are for writing 128KB data in MIPS 400mhz
sequence channel time (in microseconds)
0 1 1675
0 2 1625
0 3 1836
...
0 16 3398
0 63 1678
1 0 1702
1 1 1845
.....
3 46 17875 // large value
...
4 13 17142 ///
...
4 44 18711 /// large value
Is this behaviour ok?
I beleive this is due to deep request queue.
But when i used O_DIRECT. I got a little higher write times but it
also had such time bumps but at smaller rate.
-----------------------------------------
0 0 3184
0 1 3165
0 2 3126
...
0 52 10613 // large value
0 60 19004 // large value
results similar with O_DIRECT|O_SYNC
Can we achieve smooth write times in Linux?
I am using 2.6.10 the results are moreover same (i dont mean
numerically same but i am getting thiming difference) in both P4 3 GHZ
512MB ram and MIPS. Disk is working in UDMA 5.
--
---------------------------------------------------------------
regards
Manish Regmi
---------------------------------------------------------------
UNIX without a C Compiler is like eating Spaghetti with your mouth
sewn shut. It just doesn't make sense.
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