Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!rpi!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.arch
Subject: Re: Fast /tmp
Message-ID: <2361@crdos1.crd.ge.COM>
Date: 24 Jul 90 14:37:50 GMT
References: <10776@spool.cs.wisc.edu> <3734@auspex.auspex.com>
Reply-To: davidsen@crdos1.crd.ge.com (bill davidsen)
Organization: GE Corp R&D Center, Schenectady NY
Lines: 35


  It's interesting to note that you get a similar effect when using a
cached write-back disk controller. The kernel does the write neatly
ordered and controller reorders on position for i/o. It's not obvious to
sysadmins who install something like this that the performance gain
comes with a (slight) increase in the chance of a blown f/s on power
fail. Note that a software crash doesn't hurt the controller, so all
data will be written anyway.

  The performance gains available by doing this are great, particularly
on systems with light load, since the cpu is often not the bottleneck.

Consider this system, used for mail and news:
________________________________________________________________

CPU in seconds
  cpu[IDLE]   =          487647 ( 94.7%)   wait[IO]    =            8931
  cpu[USER]   =            8143 (  1.6%)   wait[SWAP]  =               0
  cpu[KERNEL] =           19299 (  3.7%)   wait[PIO]   =               0
I/O counts
  bread       =     286531	  bwrite      =     377804
  lread       =    8876796	  lwrite      =    3090676
  readch      = 1044977964	  writech     =  649909542
Process counts
  swapin      =          0	  swapout     =          0
  pswitch     =    5154173
  syscall     =   29242599	  sysfork     =      68658
________________________________________________________________

  Although the lack of swap indicates enough memory, I would really want
to have more before I dedicated any to ramdisk, but I suspect that just
making /tmp a ramdisk of about 8MB would help performance a lot.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
            "Stupidity, like virtue, is its own reward" -me