disk I/O, VFS hirunningspace

Gary Jennejohn gljennjohn at googlemail.com
Wed Jul 14 07:04:59 UTC 2010


On Tue, 13 Jul 2010 15:34:12 -0700
Jerry Toung <jrytoung at gmail.com> wrote:

> Hello List,
> I am on 8.0 RELEASE amd64. My system has 2 RAID arrays connected to 2
> separate
> controllers.
> My I/O throughput tests jumped by ~100MB/sec on both channels, when I
> commented out the
> following piece of code from kern/vfs_bio.c
> 
> void
> waitrunningbufspace(void)
> {
> /*
>         mtx_lock(&rbreqlock);
>         while (runningbufspace > hirunningspace) {
>                 ++runningbufreq;
>                 msleep(&runningbufreq, &rbreqlock, PVM, "wdrain", 0);
>         }
>         mtx_unlock(&rbreqlock);
> */
> }
> 
> so far, I can't observe any side effects of not running it. Am I on a time
> bomb?
> 

Rather than commenting out the code try setting the sysctl
vfs.hirunningspace to various powers-of-two.  Default seems to be
1MB.  I just changed it on the command line as a test to 2MB.

You can do this in /etc/sysctl.conf.

--
Gary Jennejohn


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