From owner-freebsd-hackers@FreeBSD.ORG  Tue Jul 13 22:58:39 2010
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From: Jerry Toung <jrytoung@gmail.com>
To: freebsd-hackers@freebsd.org
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Subject: disk I/O, VFS hirunningspace
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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?

Thank you,
Jerry